Method of crystallizing a semiconductor film using laser irradiation

ABSTRACT

There is provided an optical system for reducing faint interference observed when laser annealing is performed to a semiconductor film. The faint interference conventionally observed can be reduced by irradiating the semiconductor film with a laser beam by the use of an optical system using a mirror of the present invention. The optical system for transforming the shape of the laser beam on an irradiation surface into a linear or rectangular shape is used. The optical system may include an optical system serving to convert the laser beam into a parallel light with respect to a traveling direction of the laser beam. When the laser beam having passed through the optical system is irradiated to the semiconductor film through the mirror of the present invention, the conventionally observed faint interference can be reduced. Besides, the optical system which has been difficult to adjust can be simplified.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for manufacturing asemiconductor device having a circuit structured with a thin filmtransistor. For example, the invention relates to an apparatus formanufacturing an electro-optical device, typically a liquid crystaldisplay device, and the structure of electric equipment mounted withsuch an electro-optical device as a component. The present inventionalso relates to a method of fabricating the apparatus. Note thatthroughout this specification, the semiconductor device indicatesgeneral devices that may function by use of semiconductorcharacteristics, and that the above electro-optical device and electricequipment are categorized as the semiconductor device.

2. Description of the Related Art

In recent years, the technique of crystallizing and improving thecrystallinity of a semiconductor film formed on an insulating substratesuch as a glass substrate by laser annealing, has been widelyresearched. Silicon is often used as the above semiconductor film.

Comparing a glass substrate with a quartz substrate, which is often usedconventionally, the glass substrate has advantages of low-cost and greatworkability, and can be easily formed into a large surface areasubstrate. This is why the above research is performed. Also, the reasonfor preferably using laser annealing for crystallization resides in thatthe melting point of a glass substrate is low. Laser annealing iscapable of imparting high energy only to the semiconductor film withoutcausing much change in the temperature of the substrate.

The crystalline semiconductor film is formed from many crystal grains.Therefore, it is called a polycrystalline semiconductor film. Acrystalline semiconductor film formed by laser annealing has highmobility. Accordingly, it is actively used in, for example monolithictype liquid crystal electro-optical devices where thin film transistors(TFTs) are formed using this crystalline semiconductor film andfabricate TFTs for driving pixels and driver circuits formed on oneglass substrate.

Furthermore, a method of performing laser annealing is one in which apulse laser beam emitted from a excimer laser or the like, is processedby an optical system so that the laser beam thereof becomes a linearshape that is 10 cm long or greater or a square spot that is several cmsquare at an irradiated surface to thereby scan the laser beam (orrelatively move the irradiation position of the laser beam to theirradiated surface). Because this method is high in productivity andindustrially excellent, it is being preferably employed.

Different from when using a spot shape laser beam which requires afront, back, left, and right scan on an irradiated surface, when usingthe linear beam, the entire irradiated surface can be irradiated by thelinear beam which requires only scanning at a right angle direction tothe linear direction of the linear beam, resulting in the attainment ofa high productivity. To scan in a direction at a right angle to thelinear direction is the most effective scanning direction. Because ahigh productivity can be obtained, using the linear beam which is linearin the irradiated surface that is emitted from the pulse oscillationtype excimer laser and processing it into a linear beam by anappropriate optical system for laser annealing at present is becomingmainstream.

Shown in FIG. 1 is an example of the structure of an optical system forlinearizing the shape of a laser beam on the irradiated surface. Thisstructure is a very general one and all aforementioned optical systemsconform to the structure of the optical system shown in FIG. 1. Thisstructure of the optical system not only transforms the shape of thelaser beam in the irradiated surface into a linear shape, but alsohomogenizes the energy of the laser beam in the irradiated surface atthe same time. Generally, an optical system that homogenizes the energyof a beam is referred to as a beam homogenizer.

If the excimer laser, which is ultraviolet light, is used as the lightsource, then the core of the above-mentioned optical system may bepreferably made of, for example, entirely quartz. The reason for usingquartz resides in that a high transmittance can be obtained. Further, itis preferable to use a coating in which a 99% or more transmittance canbe obtained with respect to a wavelength of the excimer laser that isused.

The side view of FIG. 1 will be explained first. Laser beam emitted froma laser oscillator 101 is split at a right angle direction to theadvancing direction of the laser beam by cylindrical lens arrays 102 aand 102 b. The direction is referred to as a longitudinal directionthroughout the present specification. When a mirror is placed along theoptical system, the laser beams in the longitudinal direction will curvein the direction of light curved by the mirror. These laser beams inthis structure are split into 4 beams. The split laser beams are thenconverged into 1 beam by a cylindrical lens 104. Then, the convergedlaser beam are split again and reflected at a mirror 107. Thereafter,the split laser beams are again converged into 1 laser beam at anirradiated surface 109 by a doublet cylindrical lens 108. A doubletcylindrical lens is a lens that is constructed of 2 pieces ofcylindrical lenses. Thus, the energy in the width direction of thelinear laser beam is homogenized and the length of the width directionof the linear beam is also determined.

The top view of FIG. 1 will be explained next. Laser beam emitted fromthe laser oscillator 101 is split at a right angle direction to theadvancing direction of the laser beam and at a right angle direction tothe longitudinal direction by a cylindrical lens array 103. The rightangle direction is called a vertical direction throughout the presentspecification. When a mirror is placed along the optical system, thelaser beams in the vertical direction will curve in the direction oflight curved by the mirror. The laser beams in this structure is splitinto 7 beams. Thereafter, the split laser beams are converged into 1beam at the irradiated surface 109 by the cylindrical lens 104. Thus,homogenization of the energy in the longitudinal direction of the linearbeam is made and the length of the longitudinal direction is alsodetermined.

The above lenses are made of synthetic quartz for correspondence toexcimer laser. Furthermore, coating is implemented on the surfaces ofthe lenses so that the excimer laser will be well transmitted.Therefore, the transmittance of excimer laser through each lens is 99%or more.

By irradiating the linear beam linearized by the above structure of theoptical system in an overlapping manner with a gradual shift in thewidth direction thereof, laser annealing is implemented to the entiresurface of a semiconductor film to thereby crystallize the semiconductorfilm and thus its crystallinity can be enhanced.

A typical method of manufacturing a semiconductor film that is to becomethe object to be irradiated is shown next. First, for example, a 5 inchsquare Corning 1737 substrate having a thickness of 0.7 mm is preparedas the substrate. Then a 200 nm-thick SiO₂ film (silicon oxide film) isformed on the substrate and a 50 nm-thick amorphous silicon film isformed on the surface of the SiO₂ film. The substrate is exposed underan atmosphere containing nitrogen gas at a temperature of 500° C. for 1hour to thereby reduce the hydrogen concentration in the film.Accordingly, the laser resistance in the film is remarkably improved.

The XeCl excimer laser L3308 (wavelength: 308 nm, pulse width: 30 ns)manufactured by Lambda Co. is used as the laser apparatus. This laserapparatus generates a pulse oscillation laser and has the ability tooutput an energy of 500 mJ/pulse. The size of the laser beam at the exitof the laser beam is 10×30 mm (both half-width). Throughout the presentspecification, the exit of the laser beam is defined as theperpendicular plane in the advancing direction of the laser beamimmediately after the laser beam is emitted from the laser irradiationapparatus.

The shape of the laser beam generated by the excimer laser is generallyrectangular and is expressed by an aspect ratio which falls under therange of the order of 3 to 5. The intensity of the laser beam growsstronger towards the center of the beam and indicates the Gaussiandistribution. The size of the laser beam processed by the optical systemhaving the structure shown in FIG. 1 is transformed into a 125 mm×0.4 mmlinear beam having a uniform energy distribution.

When irradiating a laser beam to the above-mentioned semiconductor film,the most suitable overlapping pitch is approximately 1/10 of the beamwidth (half-width) of the linear beam. The uniformity of thecrystallinity in the film is thus improved. In the above example, thehalf-width of the linear laser beam was 0.4 mm, and therefore the pulsefrequency of the excimer laser was set to 30 hertz and the scanningspeed was set to 1.0 mm/s to thereby irradiate the laser beam. At thispoint, the energy density in the irradiated surface of the laser beamwas set to 420 mJ/cm². The method described so far is a very generalmethod employed for crystallizing a semiconductor film by using a linearbeam.

When an extremely attentive observation is made to a semiconductor filmthat has been laser annealed by using the above-mentioned linear beam,very faint interference patterns were seen in the film. The cause of theinterference patterns seen in the film resides in that the laser beam issplit and assembled in one region, and therefore the split light bringsabout interference with each other. The coherent length of the excimerlaser is about several μm to several tens of μm.

SUMMARY OF THE INVENTION

When a laser annealing is performed to a semiconductor film by using aconventional optical system, since faint interference is seen, anoptical system in which interference is suppressed is provided accordingto the present invention. Besides, although the conventional opticalsystem is complicated as shown in FIG. 1, according to the presentinvention, a uniform laser beam can be obtained by an optical systemmainly including a beam collimator for transforming a laser beam into aparallel light and a reflecting mirror, and it is also possible tosimplify the optical system for forming the laser beam having a linearor rectangular shape on an irradiation surface.

A laser beam has a feature that even if laser beams are emitted from thesame light source, they do not interfere with each other if there is anoptical path difference equal to or longer than a coherent length.First, an explanation will be made with reference to FIG. 2. FIG. 2shows a laser oscillator 201, a half mirror 202, mirrors 203 to 205, andan irradiation surface 206. It is assumed that the distance between thehalf mirror 202 and the mirror 203 is equal to the distance between themirror 204 and the mirror 205, and the distance between the mirror 203and the irradiation surface 206 is equal to the distance between themirror 205 and the irradiation surface 206. A laser beam emitted fromthe laser oscillator 201 is divided by the half mirror 202 into a laserbeam transmitted through the half mirror and traveling straight and alaser beam traveling in a direction perpendicular to the originaltraveling direction. After the laser beam bent to the perpendiculardirection is reflected by the mirror 203, it reaches the irradiationsurface 206. On the other hand, the laser beam transmitted through thehalf mirror 202 reaches the irradiation surface 206 through the mirrors204 and 205.

In this way, although the laser beams divided by the half mirror in thetwo directions are assembled again to make one beam at or in thevicinity of the irradiation surface 206, the distance from the halfmirror 202 to the mirror 204 is an optical path difference of the laserbeams divided in two. In the case where this optical path difference islonger than the coherent length of the laser beam, interference at theirradiation surface does not occur.

For example, in the case where an excimer laser is used as the laseroscillator 201, since the coherent length of the excimer laser is aboutseveral μm to several tens of μm, if the distance from the half mirror202 to the mirror 204 is several mm, the interference does not occur atthe irradiation surface 206. In the case where a YAG laser is used asthe laser oscillator 201, since the coherent length of the YAG laser islonger than the coherent length of the excimer laser, if the distancefrom the half mirror 202 to the mirror 204 is made longer than that inthe case of the excimer laser, the interference at the irradiationsurface 206 does not occur.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 are diagrams showing a side view and a top view, respectively, ofa conventional optical system that forms a linear beam;

FIG. 2 is a diagram showing the laser beam split into two directions bythe half mirror to be assembled into one on the irradiated surface;

FIG. 3 are diagrams showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 4 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 5 is a diagram showing an example of a beam collimator;

FIG. 6 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 7 is a diagram showing an example of displacement of a mirrordisclosed in the present invention;

FIG. 8 is a diagram showing an example of displacement of a mirrordisclosed in the present invention;

FIG. 9 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 10 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 11 is a diagram showing an example of displacement of a mirrordisclosed in the present invention;

FIG. 12 is a diagram showing an example of displacement of a mirrordisclosed in the present invention;

FIG. 13 is a diagram showing an example of displacement of a mirrordisclosed in the present invention;

FIG. 14 is a diagram showing the outer appearance of an AM-LCD;

FIGS. 15A to 15D are diagrams showing an example of a manufacturingprocess of a pixel TFT and a TFT of a driver circuit;

FIGS. 16A to 16D are diagrams showing an example of a manufacturingprocess of a pixel TFT and a TFT of a driver circuit;

FIGS. 17A to 17D are diagrams showing an example of a manufacturingprocess of a pixel TFT and a TFT of a driver circuit;

FIGS. 18A to 18C are diagrams showing an example of a manufacturingprocess of a pixel TFT and a TFT of a driver circuit;

FIG. 19 is a diagram showing an example of a manufacturing process of apixel TFT and a TFT of a driver circuit;

FIG. 20 is a diagram showing a top view of a pixel;

FIG. 21 is a diagram showing the cross-sectional structure of a liquidcrystal display device;

FIGS. 22A to 22C are diagrams showing an example of a manufacturingprocess of the present invention;

FIGS. 23A to 23D are diagrams showing an example of a manufacturingprocess of the present invention;

FIGS. 24A and 24B are diagrams showing the structure of an active matrixEL display device;

FIGS. 25A and 25B are diagrams showing the structure of an active matrixEL display device;

FIG. 26 is a diagram showing the structure of an active matrix ELdisplay device;

FIGS. 27A and 27B are diagrams showing the structure of an active matrixEL display device;

FIG. 28 is a diagram showing the structure of an active matrix ELdisplay device;

FIGS. 29A to 29C are diagrams showing a circuit configuration of anactive matrix EL display device;

FIGS. 30A to 30F are diagrams showing examples of an electronic device;

FIGS. 31A to 31D are diagrams showing examples of an electronic device;and

FIG. 32 is a diagram showing a laser irradiation system in accordancewith one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment Mode ofthe Invention]

An example of an optical system of the present invention is shown inFIG. 3. First, a side view of FIG. 3 will be described. A laser beamemitted from a laser oscillator 301 travels with a divergent angle. Thelaser beam is made a parallel light by a cylindrical lens 304 and acylindrical lens 305, and is converged by a mirror 306 on an irradiationsurface 307 of an object, which is held by a stage not shown in thefigure. The stage is moved in a direction perpendicular to thelongitudinal direction of the laser beam as shown by the arrow 308 inorder to treat an entire surface of the object. The cylindrical lens 304and the cylindrical lens 305 will be described later. The mirror 306 isconstructed by a plurality of plane mirrors 306 a to 306 d. Here, thenumber of the plane mirrors is made four. The energy of the linear beamin the width direction is made uniform by the mirror 306, and the lengthis determined. In the mirror 306, the position of the plane mirror 306 bis determined by determining the position of the plane mirror 306 a, andby this, the position of the plane mirror 306 c is determined, and bythis, the position of the plane mirror 306 d is determined. A method ofdetermining the positions of these plane mirrors will be describedlater. In the mirror 306, the adjacent plane mirror 306 a and the planemirror 306 b, the plane mirror 306 b and the plane mirror 306 c, theplane mirror 306 c and the plane mirror 306 d are respectively incontact with each other at end points. However, as shown in FIG. 4, itis not always necessary that the adjacent mirrors are in contact witheach other at the ends of the mirrors. A method of determining thearrangement of the respective mirrors in this case will also bedescribed later.

In the meantime, the drawings of the optical system are depicted in sucha manner that the laser beam is directed from a lower portion of thedrawing sheet to an upper portion of the drawing sheet for theconvenience of explanation. However, this relation, i.e. the relationbetween the mirror and the object to be irradiated with the laser beamcan be modified.

As the laser oscillator 301, since an excimer laser has a large outputand can oscillate a high repetition pulse of about 300 Hz under thepresent circumstances, it is often used for crystallization of asemiconductor film. In recent years, in the fabrication of a liquidcrystal display of a low temperature polysilicon TFT which has beendeveloped into a product, the excimer laser is used in a crystallizingstep of a semiconductor film. Besides, not only the excimer laser, butalso an Ar laser, YAG laser, YVO₄ laser, or the like can be used.

The function of the cylindrical lens 304 and the cylindrical lens 305for transforming the laser beam emitted from the laser oscillator 301into the parallel light will be described. In general, a laser beam hasa divergent angle. The divergent angle of the laser beam is differentamong the respective laser oscillators. For example, in the case of theexcimer laser, an exchange of a tube in a laser oscillator must be madeonce every 1 to 3 years, and further, a resonant mirror at both ends ofthe tube must be exchanged or polished once every several months to oneyear. By these operations, even in the same apparatus, the divergentangle of the laser beam is changed by 0.1 to 0.5 mrad. Also in anotherlaser oscillator, a resonant mirror must be exchanged or polished onceevery several months to one year, and by these operations, the divergentangle is changed. Since the invention disclosed in this specification isapt to receive the influence of the change of the divergent angle, it isnecessary to control this, and it becomes indispensable to provide anoptical system for forming a parallel beam which does not receive theinfluence of the change of the divergent angle. The optical system iscalled a beam collimator.

The beam collimator will be described. FIG. 5A shows one lens 501 havinga focal distance f1, and a traveling laser beam with a divergent anglebecomes a parallel light through the lens 501. When the laser beam istraced in the direction opposite to the traveling direction, it isconverged on a point apart from the lens 501 by the focal distance f1.Although FIG. 5B shows one lens 501 having the same focal distance f1 asFIG. 5A, a divergent angle of a laser beam incident on the lens 501 isdifferent from that of FIG. 5A. Even if the laser beam is traced in thedirection opposite to the traveling direction, it is not converged on apoint apart from the lens 501 by the focal distance f1. Like this, thebeam collimator formed of one lens can not cope with the change of thedivergent angle of the laser beam by the same lens, and a new lens mustbe prepared each time the divergent angle is changed, so that the costis high.

FIG. 5C shows a lens 502 and a lens 503, a traveling laser beam with adivergent angle is once converged after passing through the lens 502,and the lens 503 is disposed apart from the converged point by a focaldistance f3. In the case where such arrangement is made, a laser beamhaving a divergent angle and incident on the lens 502 is once converged,and then, it becomes a parallel light through the lens 503. AlthoughFIG. 5D uses the same lenses 502 and 503 as those of FIG. 5C, adivergent angle of an incident laser beam is different from that of FIG.5C. However, if the distance between the lens 502 and the lens 503 ischanged without changing the fact that the distance from the point onwhich the laser beam is converged after passing through the lens 502 tothe lens 503 is the focal distance f3 of the lens 503, the laser beampassing through the lens 502 and the lens 503 becomes a parallel light.

As described above, although the beam collimator of one lens can copewith only one divergent angle, if it is constructed by two lenses, itcan cope with any divergent angles. Thus, also in the case of FIG. 3, itis assumed that the divergent angle of the laser beam is changed, andtwo lenses of the cylindrical lens 304 and the cylindrical lens 305 areused for transforming a laser beam having a divergent angle into aparallel light.

Next, a top view of FIG. 3 will be described. The laser beam emittedfrom the laser oscillator 301 is divided toward a directionperpendicular to the traveling direction of the laser beam by acylindrical array lens 302. The foregoing direction is called a lateraldirection in this specification. It is assumed that when a mirror isinserted in the middle of an optical system, the lateral direction turnsto the direction of a light bent by the mirror. This structure adoptsdivision into four parts. These divided laser beams are united to makeone beam at the irradiation surface 307 by a cylindrical lens 303.

Here, a method of determining the shape of the mirror 306 will bedescribed. As shown in FIG. 6, a plane perpendicular to the irradiationsurface and parallel to the width direction of the laser beam is made anxy plane, and the longitudinal direction of the laser beam is made a Zaxis. Since FIG. 6 shows FIG. 3 three-dimensionally, reference numeralsin the drawing are the same as those of FIG. 3.

As shown in FIG. 7, a mirror 701 is constituted by a plurality of planemirrors 702 to 704, and an explanation will be made on a method ofdetermining the positions of the plane mirrors in the case whereadjacent mirrors are in contact with each other in the respectivemirrors, like the plane mirror 702 and the plane mirror 703. In FIG. 7,similarly to FIG. 6, a plane perpendicular to an irradiation surface andparallel to the width direction of a laser beam is made an xy plane, andthe longitudinal direction of the laser beam is made a z axis. Here, forsimplifying the explanation of the mirror 701, it is assumed that themirror 701 and an irradiation surface 705 are disposed at z=0.

Coordinates A(α0,β0) and B(α1, β1) of both ends of the irradiationsurface 705 in the width direction of the laser beam and an arbitrarypoint C(x₀, y₀) are determined, and an attempt is made to obtain aparabola having the end point A(α0,β0) of the irradiation surface as thefocal point and passing through the arbitrary point C(x₀, y₀). Ingeneral, an equation of a parabola is expressed byy=p(x−a)² +b  [numerical expression 1]and the coordinate of the focal point is(a, b+1/4p).  [numerical expression 2]Thus, in order to obtain the equation of the parabola having the pointA(α0, β0) as the focal point and passing through the arbitrary pointC(x₀, y₀), from the expressions (1) and (2),y ₀ =p(x ₀ −a)² +b  [numerical expression 3]a=α ₀ , b+1/4p=β ₀  [numerical expression 4]are obtained. When the expressions (3) and (4) are solved,

[numerical expression 5]

$p = {- \frac{1}{2\left( {y_{0} - {\beta_{0} \pm \sqrt{\left( {x_{0} - \alpha_{0}} \right)^{2} + \left( {y_{0} - \beta_{0}} \right)^{2}}}} \right)}}$is obtained. Here,x _(o . . . n)>α₀ (n is an integral number)  [numerical expression 6]This is a condition under which an obtained mirror does not position atthe rear side of the irradiation surface. Although the expression (5)has two solutions, here,

[numerical expression 7] (expression 5′)

$p = {- \frac{1}{2\left( {y_{0} - \beta_{0} + \sqrt{\left( {x_{0} - \alpha_{0}} \right)^{2} + \left( {y_{0} - \beta_{0}} \right)^{2}}} \right)}}$is adopted. The expression (5)′ is adopted so as to dispose the mirror701 at the position where it does not block off the laser beam in FIG.6.

Next, an attempt is made to obtain an intersection point D(x₁, y₁)between a straight line, which is parallel to a straight line passingthrough the end point A(α₀, β₀) and the arbitrary point C(x₀, y₀) andpasses through the end point B(α₁, β₁) of the irradiation surface, and atangent of the parabola at the arbitrary point C(x₀, y₀).

Since a slope y′ of the tangent of the parabola at the arbitrary pointC(x₀, y₀) isy′=2p(x ₀−α₀)  [numerical expression 8]the equation of the tangent of the parabola at the arbitrary point C(x₀,y₀) becomesy=2p(x ₀−α₀)(x−x ₀)+y ₀  [numerical expression 9]The slope of the straight line passing through the end point A(α0, β0)of the irradiation surface and the arbitrary pint C(x₀, y₀) is(y ₀−β₀)/(x ₀−α₀),  [numerical expression 10]the equation of the straight line parallel to the straight line passingthrough the end point A(α0, β0) of the irradiation surface and thearbitrary point C(x₀, y₀) and passing through the end point B(α1, β1) ofthe irradiation surface isy=[(y ₀−β₀)/(x ₀−α₀)](x−α ₁)+β₁.  [numerical expression 11]When the expressions (7) and (9) are solved to obtain the intersectionpoint,

[numerical expression 12]

$x = {- \frac{{2\; p\;{x_{0}\left( {x_{0} - \alpha_{0}} \right)}^{2}} - {\left( {x_{0} - \alpha_{0}} \right)\left( {y_{0} - \beta_{1}} \right)} - {\alpha_{1}\left( {y_{0} - \beta_{1}} \right)}}{{2\;{p\left( {x_{0} - \alpha_{0}} \right)}^{2}} - \left( {y_{0} - \beta_{1}} \right)}}$

[numerical expression 13]

$y = {- \frac{{2\; p\;\left( {x_{0} - \alpha_{0}} \right)^{2}\alpha_{1}} - {\left( {y_{0} - \beta_{1}} \right)\left\{ {y_{0} - {2{p\left( {x_{0} - \alpha_{0}} \right)}\left( {x_{0} - \alpha_{1}} \right)}} \right\}}}{{2\;{p\left( {x_{0} - \alpha_{0}} \right)}^{2}} - \left( {y_{0} - \beta_{1}} \right)}}$and the point D(x₁, y₁) is obtained. That is, when the coordinate A(α0,β0) and B(α1, β1) of both ends in the width direction of the laser beamand the arbitrary point C(x₀, y₀) are determined, and the coefficient pof the parabola passing through the arbitrary point C(x₀, y₀) isobtained using the expression (5)′, the point D(x₁, y₁) is determined bythe expressions (10) and (11). If the mirror is disposed on a linesegment connecting the arbitrary point C(x₀, y₀) and the point D(x₁,y₁), all lights reflected by this mirror are converged on theirradiation surface.

Next, an attempt is made to obtain a parabola having the end point A(α0,β0) of the irradiation surface as the focal point and passing throughthe obtained point D(x₁, y₁), and an attempt is made to obtain anintersection point E(x2, y2) between a tangent of the parabola at thepoint D(x₁, y₁) and a straight line which passes through the end pointB(α₁, β₁) of the irradiation surface and is parallel to a line passingthrough the point A(α₀, β₀) and the point D(x₁, y₁). If a mirror isdisposed on a line segment connecting the point D(x₁, y₁) and the pointE(x2, y2), all lights reflected by this mirror are converged on theirradiation surface.

As described above, if the coordinates of the irradiation surface andone arbitrary point are first determined, the positions of the mirrorscan be sequentially determined using the expressions (5)′, (10) and(11).

Although the description has been made on the case where adjacent planemirrors such as the plane mirror 702 and the plane mirror 703 are incontact with each other at the ends of the mirrors, a case where theyare not in contact with other, as shown in FIG. 4, will be described.For the description of a mirror 406 of FIG. 4, FIG. 8 is used. In FIG.8, similarly to FIG. 7, a plane perpendicular to an irradiation surfaceand parallel to the width direction of a beam is made an xy plane, andthe longitudinal direction of the beam is made a z axis. Here, forsimplifying the explanation of a mirror 801, it is assumed that themirror 801 and an irradiation surface 805 are disposed at z=0.

When n is an arbitrary positive integer, and an optical path differencefrom each of coordinates (xn, yn) and (xn+1, yn+1) of both ends of ann-th mirror to an end point A(α₀, β₀) of the irradiation surface is notsufficient, a numerical value in view of a coherent length depending onthe kind of a laser oscillator is subtracted from the y coordinate of(xn+1, yn+1), and a newly obtained coordinate is made (xn+1′, yn+1′). Bythe use of the coordinate (xn+1′, yn+1′) and the coordinates A(α0, β0)and B(α1, β1) of both ends of the irradiation surface, (xn+2, yn+2) isobtained from the expressions (5)′, (10) and (11), and when a planemirror is disposed on a line segment connecting (xn+1′, yn+1′) and(xn+2, yn+2), a sufficient optical path difference is obtained and amirror 703 by which a light is converged on the same position of theirradiation surface 704 is obtained.

Next, an example of an optical system using a mirror 906 made of aplurality of mirrors each having a paraboloid, instead of the mirror 306of FIG. 3, is shown in FIG. 9. First, a description will be made withreference to a side view of FIG. 9. A laser beam emitted from a laseroscillator 901 travels straight with a divergent angle, is made aparallel light by a cylindrical lens 904 and a cylindrical lens 905, andis converged on an irradiation surface 907 by the mirror 906. Theprinciple in which the laser beam having a divergent angle becomes theparallel light by the cylindrical lens 904 and the cylindrical lens 905is the same as the case of FIG. 3. The shape of the mirror 906 is madeof a collection of paraboloid mirrors with different curvatures, and alight is once converged on the focal point, and then, it reaches theirradiation surface. Here, the number of the paraboloid mirrors is madefour. Since the respective paraboloids have different curvatures, thefocal points are also different from one another. By these paraboloidmirrors 906 a to 906 d, the energy of a linear beam in the widthdirection is made uniform, and the length is determined. In adjacentmirrors such as a paraboloid mirror 906 a and a paraboloid mirror 906 b,although an end of the mirror may be in contact with the next mirror, itmay not be in contact with the next mirror, like a mirror 1006 of FIG.10. The arrangement of the mirror 1006 of FIG. 10 will be explainedlater.

Next, a description will be made with reference to a top view of FIG. 9.The laser beam emitted from the laser oscillator 901 is divided toward adirection perpendicular to a traveling direction of the laser beam by acylindrical array lens 902. The foregoing direction is called a lateraldirection in this specification. It is assumed that when a mirror isinserted in the middle of an optical system, the lateral direction turnsto the direction of a light bent by the mirror. This structure adoptsdivision into four parts. These divided laser beams are united to makeone beam at the irradiation surface 907 by a cylindrical lens 903.

Here, the arrangement of the mirror 1006 of FIG. 10 will be described.In FIG. 10, a plane perpendicular to an irradiation surface and parallelto the width direction of a beam is made an xy plane, and thelongitudinal direction of the laser beam is made a z axis. A method ofdetermining the arrangement of the mirror 1006 will be described. Theposition of a paraboloid mirror 1006 a is on a line segment connectingan arbitrary point and a point obtained from the arbitrary point andcoordinates of both ends in the width direction of the laser beam on anirradiation surface 1007. A numerical value in view of a coherent lengthof the laser beam is subtracted from the y coordinate of the obtainedpoint to obtain a new coordinate. The position of a paraboloid mirror1006 b is on a line segment connecting the coordinate and a pointobtained from coordinates of both ends in the width direction of thebeam on the irradiation surface 1007. When a paraboloid mirror 1006 cand a paraboloid mirror 1006 d are obtained in such a method, it ispossible to obtain the mirror 1006 in which adjacent mirrors are not incontact with each other and a sufficient optical path difference to theirradiation surface is obtained.

Embodiment 1

In this embodiment, a case where irradiation is made using an excimerlaser will be described. The basic structure of a laser irradiationapparatus of this embodiment is the same as FIG. 3, and the positions ofrespective mirrors in a mirror of the invention are concretelycalculated and are shown in FIG. 11. In FIG. 11, a plane perpendicularto an irradiation surface and parallel to the width direction of a beamis made an xy plane, and the longitudinal direction of the beam is madea z axis. Here, for simplifying the explanation of a mirror 1101, it isassumed that the mirror 1101 and an irradiation surface 1105 aredisposed at z=0.

The mirror 1101 is made of a plurality of plane mirrors 1102 to 1104.The plane perpendicular to the irradiation surface and parallel to thewidth direction of the beam is made the xy plane, and the longitudinaldirection of the beam is made the z axis. Here, for simplifying theexplanation of the mirror 1101, it is assumed that the mirror 1101 andthe irradiation surface 1105 are disposed at z=0.

Coordinates of both ends in the width direction of the beam on theirradiation surface 1105 are made (0, 200) and (0, 199). In thisspecification, it is assumed that 1 in the coordinate corresponds to 1mm. Since it is desired that the width of the laser beam obtained at theirradiation surface 1005 is made about 1 mm, the coordinates are madethose as described before. An arbitrary point is made (x₀, y₀)=(200,190), and when the end point (0, 200) of the irradiation surface isregarded as a focal point and an attempt is made to obtain a coefficientp of a parabola passing through the point (200, 190), from theexpression (5)′,p=0.00237812is obtained. Thus, when an attempt is made to obtain (x₁, y₁) by usingthe expressions (10) and (11),(x ₁ , y ₁)=(199.001, 189.050).The obtained (x₁, y₁) is regarded as a new arbitrary point, and when anattempt is made to obtain a coefficient of a parabola passing throughthis point,p=0.00237809is obtained. Thus, when an attempt is made to obtain (x2, y2) by usingthe expressions (10) and (11),(x2, y2)=(198.003, 188.105).When an attempt is made to obtain (x3, y3) in a similar method,(x3, y3)=(197.005, 187.165).

An optical path difference from each of (x₀, y₀) and (x₁, y₁) to the endpoint (0, 200) in the width direction of the beam on the irradiationsurface 1105 is

[numerical expression 14]

${y_{0} - y_{1} + \sqrt{\left( {\alpha_{0} - x_{0}} \right)^{2} + \left( {\beta_{0} - y_{0}} \right)^{2}} - \sqrt{\left( {\alpha_{0} - x_{1}} \right)^{2} + \left( {\beta_{0} - y_{1}} \right)^{2}}} = {{190 - 189.050 + \sqrt{\left( {0 - 200} \right)^{2} + \left( {200 - 190} \right)^{2}} - \sqrt{\left( {0 - 199.001} \right)^{2} + \left( {200 - 189.050} \right)^{2}}} = 1.89762}$an optical path difference from each of (x₁, y₁) and (x2, y2) to the endpoint (0, 200) in the width direction of the beam on the irradiationsurface 1105 is

[numerical expression 15]

${y_{1} - y_{2} + \sqrt{\left( {\alpha_{0} - x_{1}} \right)^{2} + \left( {\beta_{0} - y_{1}} \right)^{2}} - \sqrt{\left( {\alpha_{0} - x_{2}} \right)^{2} + \left( {\beta_{0} - y_{2}} \right)^{2}}} = {{189.050 - 188.105 + \sqrt{\left( {0 - 199.001} \right)^{2} + \left( {200 - 189.050} \right)^{2}} - \sqrt{\left( {0 - 198.003} \right)^{2} + \left( {200 - 188.105} \right)^{2}}} = 1.88760}$and an optical path difference from each of (x2, y2) and (x3, y3) to theend point (0, 200) in the width direction of the beam on the irradiationsurface 1105 is

[numerical expression 16]

${y_{2} - y_{3} + \sqrt{\left( {\alpha_{0} - x_{2}} \right)^{2} + \left( {\beta_{0} - y_{2}} \right)^{2}} - \sqrt{\left( {\alpha_{0} - x_{31}} \right)^{2} + \left( {\beta_{0} - y_{31}} \right)^{2}}} = {{188.105 - 187.165 + \sqrt{\left( {0 - 198.003} \right)^{2} + \left( {200 - 188.105} \right)^{2}} - \sqrt{\left( {0 - 197.005} \right)^{2} + \left( {200 - 187.165} \right)^{2}}} = 1.87754}$Since the coherent length of the excimer laser is about several μm toseveral tens of μm and the unit of the optical difference is mm, it islonger than the coherent length and the interference does not occur.However, in order to lengthen the light path length and to enlarge theoptical path difference, when the first coordinate (x₁, y₁) isdetermined, for example, 1 is subtracted from the y coordinate to obtaina new coordinate (x₁′, y₁′), and when an attempt is made to obtain acoordinate of the other end of the mirror based on this coordinate, amirror by which the interference is further suppressed can befabricated.

A method of fabricating the mirror will be described with reference toFIG. 12. In FIG. 12, similarly to FIG. 11, a plane perpendicular to anirradiation surface and parallel to the width direction of a laser beamis made an xy plane, and the longitudinal direction of the beam is madea z axis. Here, for simplifying the explanation of a mirror 1201, it isassumed that the mirror 1201 and an irradiation surface 1206 aredisposed at Z=0.

When coordinates of both ends in the width direction of the laser beamare made (0, 200) and (0,199), and the arbitrary point is made (x₀,y₀)=(200, 190), although (x₁, y₁)=(199.001, 189.050) is obtained asalready described, 1 is subtracted from the y coordinate to obtain (x₁′,y₁′)=(199.001, 188.050). When an attempt is made to obtain (x2, y2)based on this, (x2, y2)=(198.003, 187.110). When 1 is subtracted fromthe y coordinate, (x2′, y2′)=(198.003, 186.110) is obtained. When anattempt is made to obtain (x3, y3), (x3, y3)=(197.005, 185.180) isobtained, and the coordinate is shifted by 1 in the x direction toobtain (x3′, y3′)=(197.005, 184.180).

On the basis of the coordinates obtained in the manner as describedabove, an attempt is made to obtain the optical path difference to theend point (0, 200) of the irradiation surface 1206 in the widthdirection of the laser beam. The optical path difference between (x₀,y₀) and (x₁′, y₁′) becomes 2.84018, the optical path difference between(x₁′, y₁′) and (x2′, y2′) becomes 2.81013, and the optical pathdifference between (x2′, y2′) and (x3′, y3′) becomes 2.77999. Theoptical path difference becomes larger than that of the arrangementwhere the adjacent mirrors are in contact with each other at the endpoints, and the interference can be further suppressed.

Embodiment 2

In this embodiment, a description will be made on a case whereirradiation is made using a YAG laser. Although the basic structure of alaser irradiation apparatus of this embodiment is the same as FIG. 9,positions of mirrors are concretely calculated.

Since the coherent length of the YAG laser is longer than the coherentlength of the excimer laser, the interference can not be suppressed verymuch by only shifting a mirror by 1 mm as in FIG. 12 of Embodiment 1.Thus, it is better to shift a mirror by about 10 mm as in FIG. 13.

Similarly to Embodiment 1, coordinates of both ends in the widthdirection of a laser beam on an irradiation surface 1306 are made (0,200) and (0, 199). Since it is desired that an actual laser beam widthis made about 1 mm, the coordinate is also made such. An arbitrary pointis made (x₀, y₀)=(200, 190), and similarly to Embodiment 1, when anattempt is made to obtain (x₁, y₁) by using the expressions (10) and(11), (x₁, y₁)=(199.001, 189.050) is obtained. However, 10 is subtractedfrom the y coordinate to obtain (x₁′, y₁′)=(199.001, 179.050). When anattempt is made to obtain (x2, y2) by using this, (x2, y2)=(198.007,178.155) is obtained, and 10 is subtracted from the y coordinate toobtain (x2′, y2′)=(198.007, 168.155). When an attempt is made to obtain(x3, y3), by using this (x3, y3)=(197.019, 167.313) is obtained, and 10is subtracted from the y coordinate to obtain (x3′, y3′)=(197.019,157.313).

By using the coordinates obtained in the manner as described above, anattempt is made to obtain the optical path difference to the end point(0, 200) in the width direction of the laser beam on the irradiationsurface 1306. The optical path difference between (x₀, y₀) and (x₁′,y₁′) becomes 11.0989, the optical path difference between (x₁′, y₁′) and(x2′, y2′) becomes 10.4450, and the optical path difference between(x2′, y2′) and (x3′, y3′) becomes 9.80177, and it is understood that theinterference is suppressed in the mirror.

Embodiment 3

This embodiment will be described with reference to FIGS. 15A to 21.Here, a method of fabricating a pixel TFT of a display region and a TFTof a driver circuit provided at the periphery of the display region onthe same substrate, and a display device using the same, will bedescribed in detail in accordance with a fabricating process. However,for simplification of the explanation, a CMOS circuit as a basic circuitof a shift register circuit, a buffer circuit, or the like in a controlcircuit and an n-channel TFT forming a sampling circuit will be shown inthe drawings.

In FIG. 15A, as a substrate 1501, a low alkaline glass substrate or aquartz substrate can be used. In this embodiment, the low alkaline glasssubstrate was used. An under film 1502, such as a silicon oxide film, asilicon nitride film, or a silicon nitride oxide film, for preventingimpurity diffusion from the substrate 1501 is formed on the surface ofthis substrate 1501 on which the TFTs are to be formed. For example, bya plasma CVD method, a silicon nitride oxide film made of SiH₄, NH₃ andN₂O and having a thickness of 100 nm, and a silicon nitride oxide filmmade of SiH₄ and N₂O and having a thickness of 200 μm are laminated.

Next, a semiconductor film 1503 a having a thickness of 20 to 150 nm(preferably 30 to 80 nm) and an amorphous structure is formed by awell-known method such as plasma CVD or by sputtering. In thisembodiment, an amorphous silicon film was formed to a thickness of 55 nmby plasma CVD. As the semiconductor film having the amorphous structure,there is an amorphous semiconductor film or a microcrystallinesemiconductor film, and a compound semiconductor film having theamorphous structure, such as an amorphous silicon germanium film, may beapplied. Since the under film 1502 and the amorphous silicon film 1503 acan be formed by the same film formation method, both may becontinuously formed. After the under film is formed, when it is notexposed to the air, pollution of its surface can be prevented, and it ispossible to decrease fluctuation in characteristics of a fabricated TFTand variation in threshold voltage (FIG. 15A).

A crystalline silicon film 1503 b is formed from the amorphous siliconfilm 1503 a by using a crystallizing technique. In this embodiment, thelaser apparatus of the present invention was used, and lasercrystallization was carried out in accordance with Embodiment 1. Priorto the step of crystallization, although depending on the hydrogencontent of the amorphous silicon film, it is desirable that a heattreatment at 400 to 500° C. for about 1 hour is carried out to make thehydrogen content 5 atom % or less, and then, crystallization is made(FIG. 15B).

The crystalline silicon film 1503 b is divided into islands to formisland-like semiconductor layers 1504 to 1507. Thereafter, a mask layer1508 having a thickness of 50 to 100 nm and made of a silicon oxide filmis formed by plasma CVD or by sputtering (FIG. 15C).

Then a resist mask 1509 is provided, and for the purpose of controllingthe threshold voltage, boron (B) as an impurity element to give a p typeis added at a concentration of about 1×10¹⁶ to 5×10¹⁷ atoms/cm³ to allthe surfaces of the island-like semiconductor layers 1505 to 1507forming n-channel TFTs. Addition of boron (B) may be carried out by iondoping or may be made at the same time as the film formation of theamorphous silicon film. Although the addition of boron (B) here is notalways necessary, it is preferable to form the semiconductor layers 1510to 1512 added with boron in order to restrict the threshold voltages ofthe n-channel TFTs in a predetermined range (FIG. 15D).

For the purpose of forming an LDD region of the n-channel TFT of thedriver circuit, an impurity element to give an n type is selectivelyadded to the island-like semiconductor layers 1510 and 1511. For thatpurpose, resist masks 1513 to 1516 are formed in advance. As theimpurity element to give the n type, phosphorus (P) or arsenic (As) maybe used, and here, ion doping using phosphine (PH₃) was applied to addphosphorus (P). It is appropriate that the concentration of phosphorous(P) of formed impurity regions 1517 and 1518 is made to be in the rangeof 2×10¹⁶ to 5×10¹⁹ atoms/cm³. In this specification, the concentrationof the impurity element to give the n type contained in the impurityregions 1517 to 1519 formed here is designated by (n⁻). The impurityregion 1519 is a semiconductor layer for forming a holding capacitanceof a pixel matrix circuit, and phosphorus (P) at the same concentrationwas also added to this region (FIG. 16A).

Next, the mask layer 1508 is removed by hydrofluoric acid or the like,and a step of activating the impurity elements added in FIG. 15D andFIG. 16A is carried out. The activation can be carried out by a heattreatment in a nitrogen atmosphere at 500 to 600° C. for 1 to 4 hours,or a laser activation method. Besides, both may be carried out together.Besides, the laser irradiation in accordance with the present invention,for example, Embodiment 1 may be carried out. In this embodiment, amethod of laser activation was used, a KrF excimer laser (wavelength 248nm) was used, a linear beam was formed, an oscillation frequency of 5 to50 Hz and an energy density of 100 to 500 mJ/cm² were prepared, andscanning was made while an overlap ratio of the linear beam was made 80to 98%, so that the whole surface of the substrate on which theisland-like semiconductor layers were formed was treated. Incidentally,any irradiation conditions of the laser beam are not limited, and anoperator may suitably determine them.

A gate insulating film 1520 is formed of an insulating film having athickness of 10 to 150 nm and containing silicon by using plasma CVD orby sputtering. For example, a silicon nitride oxide film is formed to athickness of 120 nm. As the gate insulating film, a single layer or alaminate structure of another insulating film containing silicon may beused (FIG. 16B).

Next, a first conductive layer is formed to form a gate electrode.Although this first conductive layer may be formed of a single layer, alaminate structure such as two layers or three layers may be adopted asthe need arises. In this embodiment, a conductive layer (A) 1521 made ofa conductive nitride metal film and a conductive layer (B) 1522 made ofa metal film were laminated. The conductive layer (B) 1522 may be formedof an element selected from tantalum (Ta), titanium (Ti), molybdenum(Mo) and tungsten (W), an alloy containing the foregoing elements as itsmain constituents, or an alloy film of a combination of the foregoingelements (typically, Mo—W alloy film, Mo—Ta alloy film). The conductivelayer (A) 1521 is formed of tantalum nitride (TaN), tungsten nitride(WN), titanium nitride (TiN), or molybdenum nitride (MoN). For theconductive layer (A) 1521, as an alternative material, tungstensilicide, titanium silicide, or molybdenum silicide may be applied. Inthe conductive layer (B), in order to decrease the resistance, it isappropriate that the concentration of a contained impurity is decreased,and particularly with respect to the oxygen concentration, it wasappropriate that the concentration was made 30 ppm or less. For example,with respect to tungsten (W), when the oxygen concentration was made 30ppm or less, it was possible to realize a specific resistance value of20 μΩcm or less.

It is appropriate that the thickness of the conductive layer (A) is made10 to 50 nm (preferably 20 to 30 nm) and that of the conductive layer(B) 1522 is made 200 to 400 nm (preferably 250 to 350 nm). In thisembodiment, a tantalum nitride having a thickness of 30 nm was used forthe conductive layer (A) 1521, a Ta film having a thickness of 350 nmwas used for the conductive layer (B), and both were formed bysputtering. In this film formation by this sputtering, when a suitableamount of Xe or Kr is added to Ar of a gas for sputtering, it ispossible to relieve the internal stress of the formed film and toprevent the peeling of the film. Incidentally, although not shown, it iseffective to form a silicon film having a thickness of about 2 to 20 mmand doped with phosphorus under the conductive layer (A) 1521. By this,the improvement of adhesion of the conductive film formed thereon andprevention of oxidation are realized, and it is possible to prevent avery small amount of alkaline metal element contained in the conductivelayer (A) or the conductive layer (B) from diffusing into the gateinsulating film 1520 (FIG. 16C).

Next, resist masks 1523 to 1527 are formed, and the conductive layer (A)1521 and the conductive layer (B) 1522 are etched at the same time toform gate electrodes 1528 to 1531 and a capacitance wiring line 1532.The gate electrodes 1528 to 1531 and the capacitance wiring line 1532are formed of films 1528 a to 1532 a made of the conductive layer (A)and films 1528 b to 1532 b made of the conductive layer (B) in a body.At this time, the gate electrodes 1529 and 1530 formed in the drivercircuit are formed so as to overlap with part of the impurity regions1517 and 1518 through the gate insulating film 1520 (FIG. 16D).

Next, in order to form a source region and a drain region of a p-channelTFT of the driver circuit, a step of adding an impurity element to givea p type is carried out. Here, the gate electrode 1528 is used as amask, to form an impurity region in a self-aligning manner. At thistime, a region where the n-channel TFT is to be formed, is covered witha resist mask 1533. Then an impurity region 1534 is formed by ion dopingusing diborane (B₂H₆). The concentration of boron in this region is made3×10²⁰ to 3×10²¹ atoms/cm³. In this specification, the concentration ofthe impurity element to give the p type contained in the impurity region1534 formed here is designated by (p⁻) (FIG. 17A).

Next, in the n-channel TFT, an impurity region functioning as a sourceregion or a drain region was formed. Resist masks 1535 to 1537 wereformed, and an impurity element to give an n type was added to formimpurity regions 1538 to 1542. This was carried out by ion doping usingphosphine (PH₃), and the concentration of phosphorus (P) in this regionwas made 1×10²⁰ to 1×10²¹ atoms/cm³. In this specification, theconcentration of the impurity element to give the n type contained inthe impurity regions 1538 to 1542 formed here is designated by (n⁻)(FIG. 17B).

Although phosphorus (P) or boron (B) added in the former step is alreadycontained in the impurity regions 1538 to 1542, since phosphorus (P) isadded at a sufficiently high concentration as compared with that, it isnot necessary to consider the influence of phosphorus (P) or boron (B)added in the former step. Since the concentration of phosphorus (P)added in the impurity region 1538 was ½ to ⅓ of the concentration ofboron (B) added in FIG. 17A, the p-type conductivity was kept and noinfluence was exerted to the characteristics of the TFT.

Then a step of adding an impurity element to give an n type for formingan LDD region of the n-channel TFT of the pixel matrix circuit wascarried out. Here, the gate electrode 1531 was made a mask, and theimpurity element to give the n type was added by ion doping in theself-aligning manner. The concentration of added phosphorus (P) is1×10¹⁶ to 5×10¹⁸ atoms/cm³, and by adding phosphorus at theconcentration lower than the concentration of the impurity elementsadded in FIG. 16A and FIGS. 17A and 17B, only impurity regions 1543 and1544 are actually formed. In this specification, the concentration ofthe impurity element to give the n type contained in the impurityregions 1543 and 1544 is designated by (n⁻) (FIG. 17C).

Thereafter, a heat treatment step for activating the impurity elementsto give the n type or the p type added at the respective concentrationsis carried out. This step can be carried out by a furnace annealingmethod, a laser annealing method, or a rapid thermal annealing method(RTA). Here, the activation step was carried out by the furnaceannealing method. The heat treatment is carried out in a nitrogenatmosphere containing oxygen of a concentration of 1 ppm or less,preferably 0.1 ppm or less, at 400 to 800° C., typically 500 to 600° C.In this embodiment, the heat treatment at 550° C. for 4 hours wascarried out. Besides, as the substrate 1501, in the case where onehaving heat resistance such as a quartz substrate, is used, a heattreatment at 800° C. for 1 hour may be carried out. It was possible toactivate the impurity elements and to excellently form contacts betweenthe impurity regions added with the impurity elements and the channelforming regions.

In this heat treatment, in the metal films 1528 b to 1532 b for formingthe gate electrodes 1528 to 1531 and the capacitance wiring line 1532,conductive layers (C) 1528 c to 1532 c having a thickness of 5 to 80 nmfrom the surface are formed. For example, in the case where theconductive layers (B) 1528 b to 1532 b are made of tungsten (W),tungsten nitride (WN) is formed, and in the case of tantalum (Ta),tantalum nitride (TaN) can be formed. Further, the conductive layers (C)1528 c to 1532 c can be formed in the same way even when the gateelectrodes 1528 to 1531 are exposed to a plasma atmosphere containingnitrogen or nitrogen using ammonia or the like. Further, a step ofhydrogenating the island-like semiconductor layers was carried out byperforming a heat treatment in an atmosphere containing hydrogen of 3 to100% at 300 to 450° C. for 1 to 12 hours. This step is a step forterminating dangling bonds of the semiconductor layer by thermallyexcited hydrogen. As another means for hydrogenation, plasmahydrogenation (using hydrogen excited by plasma) may be carried out(FIG. 17D).

After the steps of activation and hydrogenation are ended, a secondconductive film which is made a gate wiring line is formed. It isappropriate that this second conductive film is formed of a conductivelayer (D) mainly containing aluminum (Al) or copper (Cu) as a lowresistance material, and a conductive layer (E) made of titanium (Ti),tantalum (Ta), tungsten (W), or molybdenum (Mo). In this embodiment, analuminum (Al) film containing titanium (Ti) of 0.1 to 2 weight % wasmade a conductive layer (D) 1545, and a titanium (Ti) film was formed asa conductive layer (E) 1546. It is appropriate that the conductive layer(D) 1545 is made to have a thickness of 200 to 400 nm (preferably 250 to350 nm), and the conductive layer (E) 1546 is made to have a thicknessof 50 to 200 nm (preferably 100 to 150 nm) (FIG. 18A).

For the purpose of forming gate wirings connected to the gate electrode,the conductive layer (E) 1546 and the conductive layer (D) 1545 weresubjected to an etching treatment, so that gate wiring lines 1547 and1548 and a capacitance wiring line 1549 were formed. In the etchingtreatment, a portion from the surface of the conductive layer (E) to ahalfway portion of the conductive layer (D) was first removed by dryetching using a mixture gas of SiCl₄, Cl₂ and BCl₃, and then, theconductive layer (D) was removed by a wet etching using a phosphoricacid based etching solution, so that the gate wiring lines were formedwhile a selective working property to the under film was kept (FIG.18B).

A first interlayer insulating film 1550 is formed of a silicon oxidefilm or a silicon nitride oxide film having a thickness of 500 to 1500nm, and then contact holes reaching source regions or drain regionsformed in the respective island-like semiconductor layers are formed,and source wiring lines 1551 to 1558 and drain wirings 1555 to 1558 areformed. Although not shown, in this embodiment, the electrode was made alaminate film of three-layer structure in which a Ti film having athickness of 100 nm, an aluminum film containing Ti and having athickness of 300 nm, and a Ti film having a thickness of 150 nm werecontinuously formed by sputtering.

Next, as a passivation film 1559, a silicon nitride film, a siliconoxide film, or a silicon nitride oxide film is formed to a thickness of50 to 500 nm (typically 100 to 300 nm). When hydrogenation processingwas carried out in this state, a desirable result for the improvement ofcharacteristics of the TFT was obtained. For example, it was appropriatethat a heat treatment in an atmosphere containing hydrogen of 3 to 100%was carried out at 300 to 450° C. for 1 to 12 hours, or a similar effectwas obtained even when a plasma hydrogenating method was used.Incidentally, here, an opening portion may be formed in the passivationfilm 159 at a position where a contact hole for connection of a pixelelectrode and a drain wiring is formed later (FIG. 18C).

Thereafter, a second interlayer insulating film 1560 made of organicresin is formed to a thickness of 1.0 to 1.5 μm. As the organic resin,polyimide, acryl, polyamide, polyimidoamide, BCB(benzocyclobutene) orthe like can be used. Here, polyimide of a type in which thermalpolymerization was made after application to a substrate was used, andthe film was formed through firing at 300° C. A contact hole reachingthe drain wiring line 1558 is formed in the second interlayer insulatingfilm 1560, and pixel electrodes 1561 and 1562 are formed. As the pixelelectrode, in the case where a transmission type liquid crystal displaydevice is formed, a transparent conductive film may be used, and in thecase where a reflection type liquid crystal display device is formed, ametal film may be used. In this embodiment, for the purpose of formingthe transmission type liquid crystal display device, an indium-tin oxide(ITO) film was formed to a thickness of 100 nm by sputtering (FIG. 19).

In this way, it was possible to complete the substrate including theTFTs of the driver circuit and the pixel TFT of the display region onthe same substrate. A p-channel TFT 1601, a first n-channel TFT 1602,and a second n-channel TFT 1603 were formed in the driver circuit, and apixel TFT 1604 and a holding capacitance 1605 were formed in the displayregion. In the present specification, for convenience, such a substrateis called an active matrix substrate.

FIG. 20 is a top view showing almost one pixel of the display region. Asectional structure along A-A′ shown in FIG. 20 corresponds to thesectional view of the display region shown in FIG. 19. FIG. 20 usescommon characters so that the diagram corresponds to the sectionalstructural views of FIGS. 15A to 19. The gate wiring 1548 intersectswith the semiconductor layer 1507 through a not shown gate insulatingfilm. Although not shown, a source region, a drain region, and an Loffregion made of an n⁻ region are formed in the semiconductor layer.Reference numeral 1563 designates a contact portion between the sourcewiring 1554 and a source region 1624; 1564, a contact portion betweenthe drain wiring line 1558 and a drain region 1626; and 1565, a contactportion between the drain wiring line 1558 and the pixel electrode 1561.The holding capacitance 1605 is formed of a region where a semiconductorlayer 1627 extending from the drain region 1626 of the pixel TFT 1604overlaps with the capacitance wiring lines 1532 and 1549 through thegate insulating film.

The p-channel TFT 1601 of the driver circuit includes, in theisland-like semiconductor layer 1504, a channel forming region 1606,source regions 1607 a and 1607 b, and drain regions 1608 a and 1608 b.The first n-channel TFT 1602 includes, in the island-like semiconductorlayer 1505, a channel forming region 1609, an LDD region 1610overlapping with the gate electrode 1529 (hereinafter, such an LDDregion is referred to as Lov), a source region 1611, and a drain region1612. The length of this Lov region in the channel length direction wasmade 0.5 to 3.0 μm, preferably 1.0 to 1.5 μm. The second n-channel TFT1603 includes, in the island-like semiconductor layer 1506, a channelforming region 1613, LDD regions 1614 and 1615, a source region 1616,and a drain region 1617. In this LDD region, an Lov region and an LDDregion which does not overlap with the gate electrode 1530 (hereinafter,such an LDD region is referred to as Loff) are formed, and the length ofthis Loff region in the channel length direction is 0.3 to 2.0 μm,preferably 0.5 to 1.5 μm. The pixel TFT 1604 includes, in theisland-like semiconductor layer 1507, channel forming regions 1618 and1619, Loff regions 1620 to 1623, and source or drain regions 1624 to1626. The length of the Loff region in the channel length direction is0.5 to 3.0 μm, preferably 1.5 to 2.5 μm. Further, the holdingcapacitance 1605 is formed of the capacitance wirings 1532 and 1549, theinsulating film made of the same material as the gate insulating film,and the semiconductor layer 1627 connected to the drain region 1626 ofthe pixel TFT 1604 and added with the impurity element to give the ntype. Besides, it is not necessary that the present invention is limitedto the structure of the holding capacitance shown in the embodiment. Forexample, it is also possible to use a holding capacitance of a structuredisclosed in Japanese Patent Application No. Hei. 9-316567, No. Hei.9-273444 and No. Hei. 10-254097 by the present assignee.

In FIG. 19, although the pixel TFT 1604 is made to have a double gatestructure, a single gate structure may be adopted, or a multi-gatestructure in which a plurality of gate electrodes are provided may beadopted.

A process of fabricating an active matrix liquid crystal display devicefrom the above active matrix substrate will be described. As shown inFIG. 21, an orientation film 1701 was formed over the active matrixsubstrate of the state of FIG. 19 fabricated by the above method. Ingeneral, polyimide resin is often used for the orientation film of aliquid crystal display element. A light shielding film 1703, atransparent conductive film 1704, and an orientation film 1705 wereformed on an opposite substrate 1702 at an opposite side. After theorientation film was formed, a rubbing treatment was carried out so thatliquid crystal molecules were oriented with a certain constant pre-tiltangle. Then the active matrix substrate on which the pixel matrixcircuit and the CMOS circuit are formed was bonded to the oppositesubstrate by a well-known cell assembling step through a sealingmaterial (not shown), a columnar spacer 1707 or the like. Thereafter, aliquid crystal material 1706 was injected between both substrates, andthey were completely sealed by a sealing agent (not shown). As theliquid crystal material, a well-known liquid crystal material may beused. In this way, the active matrix liquid crystal display device shownin FIG. 21 was completed.

As described above, it was possible to fabricate the active matrixliquid crystal display device in which the structures of the TFTsforming the respective circuits are optimized according to thespecification required by the pixel TFT and the driver circuit.

Embodiment 4

Referring to FIGS. 22A to 22C, an example of using another method ofcrystallization, substituting the crystallization step in Embodiment 3,is shown here in Embodiment 4.

First, the state of FIG. 22A is obtained in accordance with Embodiment3. Note that FIG. 22A corresponds to FIG. 15A.

A catalyst element for promoting crystallization (one or plural kinds ofelements selected from a group consisting of nickel, cobalt, germanium,tin, lead, palladium, iron, and copper, typically nickel) is used forperforming crystallization. Specifically, laser crystallization isperformed under a state in which the catalyst element is maintained in asurface of an amorphous silicon film to transform the amorphous siliconfilm into a crystalline silicon film. In Embodiment 4, an aqueoussolution containing nickel element (aqueous nickel acetate solution) isapplied to the amorphous silicon film by spin coating to form acatalyst-element-containing layer 1801 on the entire surface of anamorphous semiconductor film 1503 a. (FIG. 22B) The spin coating methodis employed as a means of doping nickel in Embodiment 4. However, othermethods such as evaporation and sputtering may be used for forming athin film containing a catalyst element (nickel film in the case ofEmbodiment 4) on the amorphous semiconductor film.

Employing the method of irradiating a laser stated in accordance withthe present invention, for example, Embodiment 1 of the presentinvention, a crystalline silicon film 1802 is formed next. (FIG. 22C).

By performing the rest of the process in accordance with the steps afterFIG. 15C indicated in Embodiment 3, the structure shown in FIG. 21 canbe attained.

If an island-like semiconductor layer is manufactured from the amorphoussilicon film crystallized by using a catalyst element as in Embodiment4, a very small amount of the metal element will remain in theisland-like semiconductor film. Of course, it is still possible tocomplete a TFT under this state, but preferably better to remove atleast the catalyst element that remains in a channel-forming region. Asa means of removing the catalyst element residue, there is a method ofutilizing a gettering action of phosphorous (P). The concentration ofphosphorous (P) necessary for gettering is approximately the same levelas the concentration in the impurity region (n⁺) formed in FIG. 17B.Accordingly, by means of the heat treatment in the activation step shownin FIG. 17D, the catalyst element in the channel-forming region of then-channel type TFT and the p-channel type TFT can be gettered therefrom.

There are other means for removing the catalyst element without beingparticularly limited. For example, after forming the island-shapesemiconductor layer, heat treatment is performed on the crystallinesemiconductor film with a catalyst element residue at a temperaturebetween 800 and 1150° C. (preferably between 900 and 1000° C.) for 10minutes to 4 hours (preferably between 30 minutes and 1 hour) in anoxygenous atmosphere to which 3 to 10 volume % of hydrogen chloride iscontained. Through this step, the nickel in the crystallinesemiconductor film becomes a volatile chloride compound (nickelchloride) and is eliminated in the treatment atmosphere during theoperation. In other words, it is possible to remove nickel by thegettering action of a halogen element.

A plural number of means may be used in combination to remove thecatalyst element. Also, gettering may be performed prior to theformation of the island-like semiconductor layer.

Embodiment 5

Referring to FIGS. 23A to 23D, an example of using another method ofcrystallization, substituting the crystallization step in Embodiment 3,is shown here in Embodiment 5.

First, the state of FIG. 23A is obtained in accordance with Embodiment3. Note that FIG. 23A corresponds to FIG. 15A.

First, an aqueous solution containing a catalyst element (nickel, inthis Embodiment) (aqueous nickel acetate solution) is applied to anamorphous silicon film by spin coating to form a catalystelement-containing layer 1902 on the entire surface of an amorphoussemiconductor film 1503 a. (FIG. 23B) Possible catalyst elements otherthan nickel (Ni) that can be used here are elements such as germanium(Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt (Co),platinum (Pt), copper (Cu), and gold (Au).

The spin coating method is employed as a means of doping nickel inEmbodiment 5. However, other methods such as evaporation and sputteringmay be used for forming a thin film made of a catalyst element (nickelfilm in the case of Embodiment 5) on the amorphous semiconductor film.Though the example of forming the catalyst element-containing layer 1902on the entire surface of the amorphous semiconductor film 1503 a isshown here in Embodiment 5, a mask may be formed to selectively form thecatalyst element-containing layer.

Heat treatment is performed next at a temperature between 500 and 650°C. (preferably between 550 and 600° C.) for a duration of 6 to 16 hours(preferably between 8 and 14 hours). Consequently, crystallization isadvanced and a crystalline semiconductor film (crystalline silicon filmin Embodiment 5) 1902 is formed. (FIG. 23C) In the case of selectivelyforming the catalyst element-containing layer, with an opening of themask as the starting point, crystallization advances in the directionsubstantially parallel (the direction indicated by an arrow) with thesubstrate. A crystalline silicon film that has uniform crystal growthdirection when viewed macroscopically is thus formed.

There are many defects included in the crystalline silicon filmcrystallized by the above method due to the low crystallizationtemperature, and there are cases in which it is insufficient for use asa semiconductor element material. Thus, in order to increase thecrystallinity of the crystalline silicon film, the film is irradiatedwith a laser beam using the laser irradiation method in accordance withthe present invention, for example, Embodiment 2. A crystalline siliconfilm 1903 having good crystallinity is thus formed. (FIG. 23D)

By performing the rest of the process in accordance with the steps afterFIG. 15C indicated in Embodiment 3, the structure shown in FIG. 21 canbe attained.

Note that similar to Embodiment 4, it is further preferable to removethe catalyst element that will remain at least from the channel-formingregion. Accordingly, it is also desirable that gettering be performed byusing the method indicated in Embodiment 3.

Embodiment 6

The structure of an active matrix liquid crystal display deviceindicated in Embodiment 3 is explained using the perspective view ofFIG. 14. Note that in order to give correspondence with the diagrams ofFIGS. 15A to 20, common symbols are used for FIG. 14.

In FIG. 14, an active matrix substrate is structured by a display region1706, a scanning signal driver circuit 1704, and an image signal drivercircuit 1705 formed on a glass substrate 1501. A pixel TFT 1604 isprovided in the display region, and the driver circuits formed in theperiphery thereof are structured with CMOS circuit as a base. Thescanning signal driver circuit 1704 and the image signal driver circuit1705 are connected to the pixel TFT 1604 by a gate wiring 1531 and asource wiring 1554, respectively. Further, an FPC 71 is connected to anexternal input terminal 74, and is connected via input wirings 75 and 76to the respective driver circuits. Reference symbol 1702 denotes anopposing substrate 1702.

Embodiment 7

In this embodiment, an example in which an EL (electroluminescence)display device (also called as light emitting display device) isfabricated by using the present invention will be described.

FIG. 24A is a top view of an EL display device using the presentinvention. In FIG. 24A, reference numeral 4010 designates a substrate;4011, a pixel portion; 4012, a source side driver circuit; and 4013, agate side driver circuit, and the respective driver circuits lead to anFPC 4017 through wirings 4014 to 4016 and are connected to an externalequipment.

At this time, a cover member 6000, a sealing member (also called ahousing member) 7000, and a sealant (second sealing member) 7001 areprovided so as to surround at least the pixel portion, preferably thedriver circuits and the pixel portion.

FIG. 24B is a view showing a sectional structure of the EL displaydevice of this embodiment. A driver circuit TFT (here, a CMOS circuit ofa combination of an n-channel TFT and a p-channel TFT is shown) 4022 anda pixel portion TFT 4023 (here, only a TFT for controlling a current toan EL element is shown) are formed on the substrate 4010 and an underfilm 4021. These TFTs may be formed by using a well-known structure (topgate structure or bottom gate structure).

The present invention can be used for the formation of crystallinesemiconductor layers for the driver circuit TFT 4022 and the pixelportion TFT 4023.

When the driver circuit TFT 4022 and the pixel portion TFT 4023 arecompleted by using the present invention, a pixel electrode 4027electrically connected to a drain of the pixel portion TFT 4023 and madeof a transparent conductive film is formed on an interlayer insulatingfilm (flattening film) 4026 made of resin material. As the transparentconductive film, a compound (called ITO) of indium oxide and tin oxideor a compound of indium oxide and zinc oxide can be used. After thepixel electrode 4027 is formed, an insulating film 4028 is formed, andan opening portion is formed over the pixel electrode 4027.

Next, an EL layer 4029 is formed. As the EL layer 4029, a laminatestructure or a single layer structure may be adopted by freely combiningwell-known EL materials (hole injecting layer, hole transporting layer,light emitting layer, electron transporting layer, and electroninjecting layer). A well-known technique may be used to determine thestructure. The EL material includes a low molecular material and a highmolecular (polymer) material. In the case where the low molecularmaterial is used, an evaporation method is used. In the case where thehigh molecular material is used, it is possible to use a simple methodsuch as a spin coating method, a printing method or an ink jet method.In general, the EL display device or a light emitting device referred toin the present specification may include triplet-based light emissiondevices and/or singlet-based light emission devices, for example.

In this embodiment, the EL layer is formed by the evaporation methodusing a shadow mask. Color display becomes possible by forming lightemitting layers (red light emitting layer, green light emitting layer,and blue light emitting layer), which can emit lights with differentwavelengths, for every pixel by using the shadow mask. In addition,there are a system in which a color conversion layer (CCM) and a colorfilter are combined, and a system in which a white light emitting layerand a color filter are combined, and either system may be used. Ofcourse, an EL display device of monochromatic light emission may beused.

After the EL layer 4029 is formed, a cathode 4030 is formed thereon. Itis desirable to remove moisture and oxygen existing in the interfacebetween the cathode 4030 and the EL layer 4029 to the utmost. Thus, itis necessary to make such contrivance that the EL layer 4029 and thecathode 4030 are continuously formed in vacuum, or the EL layer 4029 isformed in an inert gas atmosphere and the cathode 4030 is formed withoutreleasing to the atmosphere. In this embodiment, a film formationapparatus of a multi-chamber system (cluster tool system) is used, sothat the foregoing film formation is made possible.

Incidentally, in this embodiment, a laminate structure of a LiF (lithiumfluoride) film and an Al (aluminum) film is used for the cathode 4030.Specifically, the LiF (lithium fluoride) film having a thickness of 1 nmis formed on the EL layer 4029 by the evaporation method, and thealuminum film having a thickness of 300 nm is formed thereon. Of course,a MgAg electrode of a well-known cathode material may be used. Thecathode 4030 is connected to the wiring 4016 in a region designated by4031. The wiring 4016 is a power supply line for giving a predeterminedvoltage to the cathode 4030, and is connected to the FPC 4017 through aconductive paste material 4032.

For the purpose of electrically connecting the cathode 4030 to thewiring 4016 in the region 4031, it is necessary to form contact holes inthe interlayer insulating film 4026 and the insulating film 4028. Thesemay be formed at the time of etching the interlayer insulating film 4026(at the time of forming the contact hole for the pixel electrode) and atthe time of etching the insulating film 4028 (at the time of forming theopening portion before formation of the EL layer). When the insulatingfilm 4028 is etched, the interlayer insulating film 4026 may be etchedtogether. In this case, if the interlayer insulating film 4026 and theinsulating film 4028 are made of the same resin material, the shape ofthe contact hole can be made excellent.

A passivation film 6003, a filler 6004, and a cover member 6000 areformed to cover the surface of the EL element formed in this way.

Further, the sealing member is provided at the inside of the covermember 6000 and the substrate 4010 in such a manner as to cover the ELelement portion, and further, the sealant (second sealing member) 7001is formed at the outside of the sealing member 7000.

At this time, this filler 6004 functions also as an adhesive for bondingthe cover member 6000. As the filler 6004, PVC (polyvinyl chloride),epoxy resin, silicone resin, PVB (polyvinyl butyral) or EVA(ethylene-vinyl acetate) can be used. It is preferable that a dryingagent is provided in the inside of this filler 6004, since a moistureabsorption effect can be held.

A spacer may be contained in the filler 6004. At this time, the spacermay be made a granular material of BaO or the like, and the spaceritself may be made to have a moisture absorption property.

In the case where the spacer is provided, the passivation film 6003 canrelieve spacer pressure. In addition to the passivation film, a resinfilm or the like for relieving the spacer pressure may be provided.

As the cover member 6000, a glass plate, an aluminum plate, a stainlessplate, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinylfluoride) film, a Mylar film, a polyester film, or an acryl film can beused. In the case where PVB or EVA is used for the filler 6004, it ispreferable to use a sheet of a structure in which an aluminum foil ofseveral tens of μm is put between PVF films or Mylar films.

However, according to the direction of light emission (radiationdirection of light) from the EL element, it is necessary that the covermember 6000 has transparency.

The wiring 4016 is electrically connected to the FPC 4017 through thegap between the substrate 4010 and the sealing member 7000 or thesealant 7001. Incidentally, here, although the description has been madeon the wiring line 4016, the other wiring lines 4014 and 4015 are alsoelectrically connected to the FPC 4017 through a space under the sealingmember 7000 and the sealant 7001 in the same way.

Embodiment 8

In this embodiment, an example in which an EL display device differentfrom Embodiment 7 is fabricated by using the present invention will bedescribed with reference to FIGS. 25A and 25B. Since the same referencenumerals as those of FIGS. 24A and 24B designate the same portions, theexplanation is omitted.

FIG. 25A is a top view of an EL display device of this embodiment, andFIG. 25A is a sectional view taken along line A-A′ of FIG. 25A.

In accordance with Embodiment 7, steps are carried out until apassivation film 6003 covering the surface of an EL element is formed.

Further, a filler 6004 is provided so as to cover the EL element. Thisfiller 6004 functions also as an adhesive for bonding a cover member6000. As the filler 6004, PVC (polyvinyl chloride), epoxy resin,silicone resin, PVB (polyvinyl butyral) or EVA (ethylene-vinyl acetate)can be used. It is preferable that a drying agent is provided in theinside of this filler 6004, since a moisture absorption effect can beheld.

A spacer may be contained in the filler 6004. At this time, the spacermay be made a granular material of BaO or the like, and the spaceritself may be made to have a moisture absorption property.

In the case where the spacer is provided, the passivation film 6003 canrelieve spacer pressure. In addition to the passivation film, a resinfilm or the like for relieving the spacer pressure may be provided.

As the cover member 6000, a glass plate, an aluminum plate, a stainlessplate, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinylfluoride) film, a Mylar film, a polyester film, or an acryl film can beused. In the case where PVB or EVA is used for the filler 6004, it ispreferable to use a sheet of a structure in which an aluminum foil ofseveral tens of μm is put between PVF films or Mylar films.

However, according to the direction of light emission (radiationdirection of light) from the EL element, it is necessary that the covermember 6000 has transparency.

Next, after the cover member 6000 is bonded by using the filler 6004, aframe member 6001 is attached so as to cover the side (exposed surface)of the filler 6004. The frame member 6001 is bonded by a sealing member(functioning as an adhesive) 6002. At this time, as the sealing member6002, although it is preferable to use a photo-curing resin, if heatresistance of the EL layer permits, a thermosetting resin may be used.Incidentally, it is desirable that the sealing member 6002 is a materialwhich is as impermeable as possible to moisture and oxygen. A dryingagent may be added in the inside of the sealing member 6002.

A wiring line 4016 is electrically connected to an FPC 4017 through agap between the sealing member 6002 and a substrate 4010. Here, althoughdescription has been made on the wiring 4016, other wirings 4014 and4015 are also electrically connected to the FPC 4017 through a spaceunder the sealing member 6002 in the same manner.

Embodiment 9

The present invention can be used for the manufacture of TFTs in an ELdisplay panel made of a structure like Embodiment 7 or Embodiment 8.Here, a more detailed sectional structure of a pixel portion is shown inFIG. 26, its upper structure is shown in FIG. 27A, and its circuitdiagram is shown in FIG. 27B. In FIGS. 26, 27A and 27B, since commoncharacters are used, reference may be made to one another.

In FIG. 26, a switching TFT 3502 provided on a substrate 3501 is formedby using an NTFT of the present invention (see Embodiments 1 to 6). Inthis embodiment, although a double gate structure is used, since thereis no big difference in the structure and fabricating process,explanation is omitted. However, a structure in which two TFTs areessentially connected in series with each other is obtained by adoptingthe double gate structure, and there is a merit that an off currentvalue can be decreased. Incidentally, although the double gate structureis adopted in this embodiment, a single gate structure may be adopted,or a triple gate structure or a multi-gate structure having more gatesmay be adopted. Further, it may be formed by using a PTFT of the presentinvention.

A current controlling TFT 3503 is formed by using an NTFT. At this time,a drain wiring 35 of the switching TFT 3502 is electrically connected toa gate electrode 37 of the current controlling TFT. A wiring designatedby 38 is a gate wiring for electrically connecting gate electrodes 39 aand 39 b of the switching TFT 3502.

At this time, since the current controlling TFT 3503 is an element forcontrolling the amount of current flowing through an EL element, a largecurrent flows, and it is an element having high fear of deteriorationdue to heat or deterioration due to hot carriers. Thus, it is veryeffective to adopt a structure in which an LDD region is provided at adrain side of the current controlling TFT so as to overlap with a gateelectrode through a gate insulating film.

In this embodiment, although the current controlling TFT 3503 is shownas a single gate structure, a multi-gate structure in which a pluralityof TFTs are connected in series with each other may be adopted. Further,such a structure may be adopted that a plurality of TFTs are connectedin parallel with each other to essentially divide a channel formingregion into plural portions, so that radiation of heat can be made athigh efficiency. Such structure is effective as a countermeasure againstdeterioration due to heat.

Further, as shown in FIG. 27A, the wiring which becomes the gateelectrode 37 of the current controlling TFT 3503 overlaps with a drainwiring 40 of the current controlling TFT 3503 through an insulating filmin a region designated by 3504. At this time, a capacitor is formed inthe region 3504. This capacitor 3504 functions as a capacitor forholding voltage applied to the gate of the current controlling TFT 3503.Incidentally, the drain wiring 40 is connected to a current supply line(power source line) 3506 and a constant voltage is always applied.

A first passivation film 41 is provided on the switching TFT 3502 andthe current controlling TFT 3503, and a flattening film 42 made of aresin insulating film is formed thereon. It is very important to flattena stepped portion due to the TFT by using the flattening film 42. Sincean EL layer formed later is very thin, there is a case where poor lightemission occurs due to the existence of the stepped portion. Thus, it isdesirable to conduct flattening prior to formation of a pixel electrodeso that the EL layer can be formed on the flattest possible surface.

Reference numeral 43 designates a pixel electrode (cathode of the ELelement) made of a conductive film having high reflectivity, and iselectrically connected to the drain of the current controlling TFT 3503.As the pixel electrode 43, it is preferable to use a low resistanceconductive film, such as an aluminum alloy film, a copper alloy film ora silver alloy film, or a laminate film of those. Of course, a laminatestructure with another conductive film may be adopted.

A light emitting layer 45 is formed in a groove (corresponding to apixel) formed by banks 44 a and 44 b made of insulating films(preferably resin). Incidentally, here, although only one pixel isshown, light emitting layers corresponding to respective colors of R(red), G (green) and B (blue) may be separately formed. As an organic ELmaterial used for the light emitting layer, a conjugated polymermaterial is used. As a typical polymer material, polyparaphenylenevinylene (PPV) system, polyvinylcarbazole (PVK) system, polyfluorenesystem and the like are enumerated.

Although various types exist as the PPV organic EL material, forexample, a material as disclosed in “H. Shenk, H. Becker, O Gelsen, E.Kluge, W. Kreuder, and H. Spieitzer, “Polymers for Light EmittingDiodes”, Euro Display, Proceedings, 1999, p. 33-37” or Japanese PatentApplication Laid-open No. Hei. 10-92576 may be used.

As a specific light emitting layer, it is appropriate thatcyanopolyphenylenevinylene is used for a light emitting layer emittingred light, polyphenylenevinylene is used for a light emitting layeremitting green light, and polyphenylenevinylene or polyalkylphenylene isused for a light emitting layer emitting blue light. It is appropriatethat the film thickness is made 30 to 150 nm (preferably 40 to 100 nm).

However, the above examples are only examples of the organic EL materialwhich can be used for the light emitting layer, and it is not necessaryto limit the invention to these. The EL layer (layer in which lightemission and movement of carriers for that are performed) may be formedby freely combining a light emitting layer, a charge transporting layerand a charge injecting layer.

For example, although this embodiment shows the example in which thepolymer material is used for the light emitting layer, a low molecularorganic EL material may be used. It is also possible to use an inorganicmaterial, such as silicon carbide, as the charge transporting layer orthe charge injecting layer. As the organic EL material or inorganicmaterial, a well-known material can be used.

This embodiment adopts the EL layer of a laminate structure in which ahole injecting layer 46 made of PEDOT (polythiophene) or PAni(polyaniline) is provided on the light emitting layer 45. An anode 47made of a transparent conductive film is provided on the hole injectinglayer 46. In the case of this embodiment, since light generated in thelight emitting layer 45 is radiated to an upper surface side (to theupper side of the TFT), the anode must be translucent. As thetransparent conductive film, a compound of indium oxide and tin oxide ora compound of indium oxide and zinc oxide can be used. However, sincethe film is formed after the light emitting layer and the hole injectinglayer having low heat resistance is formed, it is preferable that filmformation can be made at the lowest possible temperature.

At the point when the anode 47 has been formed, an EL element 3505 iscompleted. Incidentally, the EL element 3505 here indicates a capacitorformed of the pixel electrode (cathode) 43, the light emitting layer 45,the hole injecting layer 46 and the anode 47. As shown in FIG. 27A,since the pixel electrode 43 is almost coincident with the area of thepixel, the whole pixel functions as the EL element. Thus, use efficiencyof light emission is very high, and bright image displaying becomespossible.

In this embodiment, a second passivation film 48 is further provided onthe anode 47. As the second passivation film 48, a silicon nitride filmor a silicon nitride oxide film is desirable. This object is to insulatethe EL element from the outside, and has both the meaning of preventingdeterioration due to oxidation of the organic EL material and themeaning of suppressing degassing from the organic EL material. By this,the reliability of the EL display device is raised.

As described above, the EL display panel includes the pixel portion madeof the pixel of the structure as shown in FIG. 26, and includes theswitching TFT having a sufficiently low off current value and thecurrent controlling TFT resistant to hot carrier injection. Thus, it ispossible to obtain the EL display panel which has high reliability andcan make excellent image display.

Incidentally, the structure of this embodiment can be freely combinedwith the structure of Embodiments 1 to 6. Further; it is effective touse the EL display panel of this embodiment as a display portion of anelectronic equipment.

Embodiment 10

In this embodiment, a description will be made on a structure in whichthe structure of the EL element 3505 is inverted in the pixel portionshown in Embodiment 9. FIG. 28 is used for the description.Incidentally, points different from the structure of FIG. 26 are only aportion of an EL element and a current controlling TFT, the otherexplanation is omitted.

In FIG. 28, a current controlling TFT 3503 is formed by using a PTFT.With respect to a fabricating process, reference may be made toEmbodiments 1 to 9.

In this embodiment, a transparent conductive film is used as a pixelelectrode (anode) 50. Specifically, a conductive film made of a compoundof indium oxide and zinc oxide is used. Of course, a conductive filmmade of a compound of indium oxide and tin oxide may be used.

After banks 51 a and 51 b made of insulating films are formed, a lightemitting layer 52 made of polyvinylcarbazole is formed by solutionapplication. An electron injecting layer 53 made of potassiumacetylacetonate (expressed as acacK), and a cathode 54 made of aluminumalloy are formed thereon. In this case, the cathode 54 functions also asa passivation film. In this way, an EL element 3701 is formed.

In the case of this embodiment, light generated in the light emittinglayer 52 is radiated, as indicated by an arrow, to the substrate onwhich TFTs are formed.

Incidentally, the structure of this embodiment can be freely combinedwith the structure of Embodiments 1 to 6. Further, it is effective touse the EL display panel of this embodiment as a display portion of anelectronic equipment.

Embodiment 11

In this embodiment, an example of a case where a pixel is made to have astructure different from the circuit diagram shown in FIG. 27B will bedescribed with reference td FIGS. 29A to 29C. In this embodiment,reference numeral 3801 designates a source wiring of a switching TFT;3803, a gate wiring of the switching TFT 3802; 3804, a currentcontrolling TFT; 3805, a capacitor; 3806, 3808, current supply lines;and 3807, an EL element.

FIG. 29A shows an example in which the current supply line 3806 is madecommon between two pixels. That is, it is characterized in that the twopixels are formed to become axisymmetric with respect to the currentsupply line 3806. In this case, since the number of power supply linescan be decreased, the pixel portion can be made further fine.

FIG. 29B shows an example in which the current supply line 3808 isprovided in parallel with the gate wiring 3803. Incidentally, althoughFIG. 29B shows the structure in which the current supply line 3808 doesnot overlap with the gate wiring 3803, if both are wirings formed indifferent layers, they can be provided so that they overlap with eachother through an insulating film. In this case, since an occupied areacan be made common to the power supply 3808 and the gate wiring 3803,the pixel portion can be further made fine.

The structure of FIG. 29C is characterized in that the current supplyline 3808 is provided in parallel with gate wirings 3803 a and 3803 bsimilarly to the structure of FIG. 29B, and further, two pixels areformed so they become axisymmetric with respect to the current supplyline 3808. Besides, it is also effective to provide the current supplyline 3808 in such a manner that it overlaps with either one of the gatewirings 3803 a and 3803 b. In this case, since the number of powersupply lines can be decreased, the pixel portion can be made furtherfine.

Incidentally, the structure of this embodiment can be freely combinedwith the structure of Embodiments 1 to 10. Besides, it is effective touse the EL display panel having the pixel structure of this embodimentas a display portion of an electronic equipment.

Embodiment 12

Although FIGS. 27A and 27B of Embodiment 9 show the structure in whichthe capacitor 3504 is provided to hold the voltage applied to the gateof the current controlling TFT 3503, the capacitor 3504 can also beomitted. In the case of Embodiment 9, since an NTFT as shown inEmbodiments 1 to 12 is used as the current controlling TFT 3503, itincludes the LDD region provided so as to overlap with the gateelectrode through the gate insulating film. Although a parasiticcapacitance generally called a gate capacitance is formed in thisoverlapping region, this embodiment is characterized in that thisparasitic capacitance is positively used instead of the capacitor 3504.

Since the capacity of this parasitic capacitance is changed by theoverlapping area of the gate electrode and the LDD region, it isdetermined by the length of the LDD region contained in the overlappingregion.

Also in the structures shown in FIGS. 29A, 29B and 29C of Embodiment 11,the capacitor 3805 can be similarly omitted.

Incidentally, the structure of this embodiment can be freely combinedwith the structure of Embodiments 1 to 11. Besides, it is effective touse the EL display panel having the pixel structure of this embodimentas a display portion of an electronic equipment of Embodiments 13 to 15.

Embodiment 13

The present invention may be applied to all conventional IC techniques.That is, it is applicable to all semiconductor circuits now incirculation in the markets. For example, the present invention may beapplied to a microprocessor integrated on one chip, such as a RISCprocessor, a ASIC processor, or a signal processing circuit, typically adriver circuit for liquid crystals (such as a D/A converter, a γcorrection circuit, a signal dividing circuit), and high frequencycircuits for mobile equipment (portable phone, PHS, mobile computer).

Further, a semiconductor circuit such as a microprocessor is mounted invarious kinds of electronic equipment functioning as central circuit. Astypical electronic equipment, a personal computer, a portableinformation terminal, or other household appliances may be enumerated.Additionally, a computer for controlling vehicles (an automobile, atrain, and so forth) may be given. The present invention is applicableto these types of semiconductor devices.

Any of the constitutions of Embodiments 1 through 12 may be adopted formanufacturing the semiconductor device indicated in Embodiment 13, orthe constitutions of the respective embodiments may be freely combined.

Embodiment 14

TFTs formed through carrying out the present invention may be applied tovarious electro-optical devices. Namely, the present invention may beembodied in all the electronic equipments that incorporate thoseelectro-optical devices as display medium.

As such an electronic equipment, a video camera, a digital camera, ahead mount display (goggle-type display), a wearable display, anavigation system for vehicles, a personal computer, and a portableinformation terminal (a mobile computer, a cellular phone, or anelectronic book, etc.) may be enumerated. Examples of those are shown inFIGS. 30A to 30F.

FIG. 30A shows a personal computer comprising a main body 2001, an imageinputting portion 2002, a display portion 2003, and a key board 2004.The present invention is applicable to the image inputting portion 2002,the display portion 2003, and other signal control circuits.

FIG. 30B shows a video camera comprising a main body 2101, a displayportion 2102, a voice input portion 2103, operation switches 2104, abattery 2105, and an image receiving portion 2106. The present inventionis applicable to the display portion 2102, the voice input portion 2103,and other signal control circuits.

FIG. 30C shows a mobile computer comprising a main body 2201, a cameraportion 2202, an image receiving portion 2203, an operation switch 2204,and a display portion 2205. The present invention is applicable to thedisplay portion 2205 and other signal control circuits.

FIG. 30D shows a goggle-type display comprising a main body 2301, adisplay portion 2302 and arm portions 2303. The present invention isapplicable to the display portion 2302 and other signal controlcircuits.

FIG. 30E shows a player that employs a recording medium in whichprograms are recorded (hereinafter referred to as a recording medium),and comprises a main body 2401, a display portion 2402, a speakerportion 2403, a recording medium 2404, and an operation switch 2405.Incidentally, this device uses as the recording medium a DVD (digitalversatile disc), a CD and the like to serve as a tool for enjoying musicor movies, for playing video games and for connecting to the Internet.The present invention is applicable to the display unit 2402 and othersignal control circuits.

FIG. 30F shows a digital camera comprising a main body 2501, a displayunit 2502, an eye piece section 2503, operation switches 2504, and animage receiving unit (not shown) and the like. The present invention isapplicable to the display portion 2502 and other signal controlcircuits.

As described above, application fields of the present invention isextremely broad, and is capable of being applied to every field ofelectronic equipment. In addition, the electronic equipment according tothe present embodiment can be embodied by using any constitutioncomprising any combination of Embodiment 1 to 12.

Embodiment 15

TFTs formed through carrying out the present invention may be applied tovarious electro-optical devices. Namely, the present invention may beembodied in all the manufacturing processes for the electronicequipments that incorporate those electro-optical devices as displaymedium.

As such an electronic equipment, a projector (rear type or front type orthe like) may be enumerated. Examples of those are shown in FIGS. 31A to31D.

FIG. 31A shows a front-type projector comprising a display device 2601,a screen 2602. The present invention is applicable to a display deviceand other signal control circuits.

FIG. 31B shows a rear-type projector comprising a main body 2701, adisplay device 2702, a mirror 2703, and a screen 2704. The presentinvention is applicable to the display device and other signal controlcircuits.

FIG. 31C is a diagram showing an example of the structure of the displaydevices 2601 and 2702 in FIGS. 31A and 31B. The projection device 2601or 2702 comprises a light source optical system 2801, mirrors 2802 and2804 to 2806, dichroic mirrors 2803, a prism 2807, liquid crystaldisplay device 2808, phase difference plates 2809, and a projectionoptical system 2810. The projection optical system 2810 consists of anoptical system including a projection lens. This embodiment shows anexample of three plate type, but is not particularly limited thereto.For instance, the invention may be applied also to single plate type.Further, in the light path indicated by an arrow in FIG. 31C, an opticalsystem such as an optical lens, a film having a polarization function, afilm for adjusting a phase difference and an IR film may be provided ondiscretion of a person who carries out the invention.

FIG. 31D is a diagram showing an example of the structure of the lightsource optical system 2801 in FIG. 31C. In this embodiment, the lightsource optical system 2801 comprises a reflector 2811, light source2812, lens arrays 2813 and 2814, a polarization conversion element 2815,and a condenser lens 2816. The light source optical system shown in FIG.31D is an example thereof, and is not particularly limited. Forinstance, on discretion of a person who carries out the invention, thelight source optical system may be provided with an optical system suchas an optical lens, a film having a polarization function, a film foradjusting the phase difference and an IR film.

As described above, application fields of the present invention isextremely broad, thereby being capable of applying the present inventionto every field of electronic equipment. In addition, the electronicequipment according to the present embodiment can be embodied by usingany constitution comprising any combination of Embodiment 1 to 12.

Embodiment 16

The Embodiment 16 is directed to a laser irradiation system utilizingthe laser irradiation apparatus of the present invention for massproduction. FIG. 32 is a top view of the laser irradiation system ofthis embodiment.

A substrate is transferred from a load/unload chamber 9001 by a robotarm 9003 provided in a transfer chamber 9002. At first, the substrate isaligned to a proper position in an alignment chamber 9004 and then it istransferred to a preheat chamber 9005 where the substrate is heated to apredetermined temperature, for example, 300° C. by using an infraredlamp heater. Thereafter, the substrate is transferred to a laserirradiation chamber 9007 through a gate valve 9006, following which thegate valve 9006 is closed.

The laser beam emitted from the oscillator 9000 is directed to thesubstrate provided in the laser irradiation chamber 9007 through anoptical system 9009 and a quartz window 9010. Any optical system whichhas been described in the preferred embodiments, for example, that shownin FIGS. 3 to 13 may be used as the optical system 9009.

Before the irradiation of the laser beam, the laser irradiation chambermay be evacuated to a high degree of a vacuum, for example, to 10⁻³ Paby using a vacuum pump 9011. Alternatively, the irradiation chamber isprovided with a desired atmosphere by using the vacuum pump 9011 and agas bomb 9012.

The substrate is scanned by utilizing the moving mechanism 9013 whileirradiating the line-shaped laser beam, thereby, irradiating the entiresurface of the substrate with the laser beam. Optionally, an infraredlight may be simultaneously directed to a portion of the substrateirradiated with the laser beam by using an IR lamp.

After the irradiation of the laser beam, the substrate is transferred toa cooling chamber 9008 where the substrate is gradually cooled, and thenthe substrate is returned to the load/unload chamber 9001 through thealignment chamber 9004. By repeating the foregoing steps, manysubstrates can be treated with the laser beam efficiently.

By using the laser irradiation apparatus of the present invention, theconventionally observed faint interference can be reduced. Besides, itis possible to simplify the optical system in which adjustment has beenconventionally difficult.

Further, although a lens through which a laser beam is transmitted isdeteriorated and becomes unusable as it is used, a mirror is differentfrom the lens since the laser beam does not transmit but the laser beamis reflected on the surface of the mirror, so that the deterioration isrestricted to only the surface. Thus, even if the mirror is used for along term, if coating of the surface of the mirror is again made, it canbe used again and is economical. Besides, the mirror is effective sinceaberration as in the lens is not produced. Further, if the mirror ismade a movable one by a micrometer or the like, a fine adjustmentbecomes possible, which is convenient.

In the preferred embodiments as described above, a line-shaped laserbeam (linear laser beam) or a rectangular-shaped laser beam are mainlydescribed. However, the optical system of the present invention can beapplied to other types of laser beams having a different beam shape.Also, in the preferred embodiments described above, the optical systemof the present invention is used to reduce the interference in a widthdirection of a line-shaped laser beam. However, if desired, it ispossible to reduce an interference in a length-wise direction of theline-shaped laser beam by utilizing a similar optical system of thepresent invention. Also, it is to be understood that the beam collimatoris not limited to the particular structures disclosed in the preferredembodiments of the invention. Further, if a laser beam having an enoughsmall divergent can be obtained, the present invention can be achievedwithout using a beam collimator.

1. A method of manufacturing a semiconductor device comprising: emittinga first laser beam from a laser oscillator having a cross sectionperpendicular to a propagation direction of the first laser beam;forming at least second and third laser beams by using at least firstand second mirrors, respectively by dividing the first laser beam;converging said at least second and third laser beams to obtain aconverged laser beam on a same irradiation area of a semiconductor filmwherein an energy distribution of the converged laser beam is betterthan that of the first laser beam; and moving a relative position of theirradiation area of the semiconductor film, thereby crystallizing thesemiconductor film, wherein a difference of optical path lengths betweensaid at least second and third laser beams is larger than a coherentlength of said first laser beam.
 2. The method of manufacturing asemiconductor device according to claim 1 further comprising making saidfirst laser beam as emitted from said laser oscillator a parallel laserbeam before the step of dividing said first laser beam.
 3. The method ofmanufacturing a semiconductor device according to claim 1 wherein saidfirst laser beam is a YAG laser beam.
 4. The method of manufacturing asemiconductor device according to claim 1 wherein said first laser beamis a YVO₄ laser beam.
 5. The method of manufacturing a semiconductordevice according to claim 1 wherein only the second laser beam isreflected by the first mirror and only the third laser beam is reflectedby the second mirror.
 6. The method of manufacturing a semiconductordevice according to claim 1 further comprising a step of expanding thecross section of the first laser beam in a longitudinal direction of thecross section.
 7. The method of manufacturing a semiconductor deviceaccording to claim 1, wherein each of the first and the second mirrorshas a curvature.
 8. The method of manufacturing a semiconductor deviceaccording to claim 1, wherein each of the second and the third laserbeams is totally reflected.
 9. A method of manufacturing a semiconductordevice comprising: forming a semiconductor film over a substrate;emitting a first laser beam from a laser oscillator having a crosssection perpendicular to a propagation direction of the first laserbeam; forming at least second and third laser beams by using at leastfirst and second mirrors, respectively by dividing the first laser beam;directing said at least second and third laser beams to a same portionof said semiconductor film to obtain one united laser beam at saidsemiconductor film wherein an energy distribution of said one unitedlaser beam is better than that of the first laser beam; and moving saidsubstrate relative to said one united laser beam in order to irradiatesaid semiconductor film with said one united laser beam, therebycrystallizing the semiconductor film, wherein a difference of opticalpath lengths between said at least second and third laser beams islarger than a coherent length of said first laser beam.
 10. The methodof manufacturing a semiconductor device according to claim 9 whereinsaid first laser beam is a YAG laser beam.
 11. The method ofmanufacturing a semiconductor device according to claim 9 wherein saidfirst laser beam is a YVO₄ laser beam.
 12. The method of manufacturing asemiconductor device according to claim 9 wherein only the second laserbeam is reflected by the first mirror and only the third laser beam isreflected by the second mirror.
 13. The method of manufacturing asemiconductor device according to claim 9 further comprising a step ofexpanding the cross section of the first laser beam in a longitudinaldirection of the cross section.
 14. The method of manufacturing asemiconductor device according to claim 9, wherein each of the first andthe second mirrors has a curvature.
 15. The method of manufacturing asemiconductor device according to claim 9, wherein each of the secondand the third laser beams is totally reflected.
 16. A method ofmanufacturing a semiconductor device comprising: forming a semiconductorfilm over a substrate; providing a first laser beam having a crosssection perpendicular to a propagation direction of the first laserbeam; directing the first laser beam to at least first and secondmirrors; reflecting the first laser beam to form at least second andthird laser beams by the at least first and second mirrors, therebyconverging the at least second and third laser beams to obtain aconverged laser beam on a same irradiation area of the semiconductorfilm; and moving said substrate relative to said converged laser beam inorder to irradiate said semiconductor film with said converged laserbeam, thereby crystallizing the semiconductor film, wherein a differenceof optical path lengths between the plurality of divided laser beams islarger than a coherent length of said laser beam.
 17. The method ofmanufacturing a semiconductor device according to claim 16 wherein saidfirst laser beam is a YAG laser beam.
 18. The method of manufacturing asemiconductor device according to claim 16 wherein said first laser beamis a YVO₄ laser beam.
 19. The method of manufacturing a semiconductordevice according to claim 16 further comprising a step of expanding thecross section of the first laser beam in a longitudinal direction of thecross section.
 20. The method of manufacturing a semiconductor deviceaccording to claim 16, wherein each of the first and the second mirrorshas a curvature.
 21. The method of manufacturing a semiconductor deviceaccording to claim 16, wherein each of the second and third laser beamsis totally reflected.
 22. A method of manufacturing a semiconductordevice comprising: providing a first laser beam having a cross sectionperpendicular to a propagation direction of the first laser beam;directing the first laser beam to at least first and second mirrors;reflecting the first laser beam to form at least second and third laserbeams by the at least first and second mirrors, wherein the first andsecond mirrors are arranged so that the at least second and third laserbeams are converged wherein an energy distribution of the convergedlaser beam is better than that of the first laser beam; and scanning asemiconductor film with the converged laser beam, thereby crystallizingthe semiconductor film, wherein an optical path length differencebetween the at least second and third laser beams is longer than acoherent length of the first laser beam.
 23. The method of manufacturinga semiconductor device according to claim 22 wherein said first laserbeam is a YAG laser beam.
 24. The method of manufacturing asemiconductor device according to claim 22 wherein said first laser beamis a YVO₄ laser beam.
 25. The method of manufacturing a semiconductordevice according to claim 22 wherein only the second laser beam isreflected by the first mirror and only the third laser beam is reflectedby the second mirror.
 26. The method of manufacturing a semiconductordevice according to claim 22 further comprising expanding the crosssection of the first laser beam in a longitudinal direction of the crosssection.
 27. The method of manufacturing a semiconductor deviceaccording to claim 22, wherein each of the first and the second mirrorshas a curvature.
 28. The method of manufacturing a semiconductor deviceaccording to claim 22, wherein each of the second and the third laserbeams is totally reflected.
 29. A method of manufacturing asemiconductor device comprising: emitting a first laser beam from alaser oscillator; forming at least second and third laser beams by usingat least first and second mirrors, respectively by dividing the firstlaser beam; converging said at least second and third laser beams toobtain a converged laser beam on a same irradiation area of asemiconductor film wherein an energy distribution of the converged laserbeam is better than that of the first laser beam; and moving a relativeposition of the irradiation area of the semiconductor film, therebycrystallizing the semiconductor film.
 30. The method of manufacturing asemiconductor device according to claim 29, wherein each of the firstand the second mirrors has a curvature.
 31. The method of manufacturinga semiconductor device according to claim 29, wherein each of the secondand the third laser beams is totally reflected.
 32. A method ofmanufacturing a semiconductordevice comprising: forming a semiconductorfilm over a substrate; emitting a first laser beam from a laseroscillator; forming at least second and third laser beams by using atleast first and second mirrors, respectively by dividing the first laserbeam; directing said at least second and third laser beams to a sameportion of said semiconductor film to obtain one united laser beam atsaid semiconductor film wherein an energy distribution of said oneunited laser beam is better than that of the first laser beam; andmoving said substrate relative to said one united laser beam in order toirradiate said semiconductor film with said one united laser beam,thereby crystallizing the semiconductor film.
 33. The method ofmanufacturing a semiconductor device according to claim 32, wherein eachof the first and the second mirrors has a curvature.
 34. The method ofmanufacturing a semiconductor device according to claim 32, wherein eachof the second and the third laser beams is totally reflected.
 35. Amethod of manufacturing a semiconductor device comprising: forming asemiconductor film over a substrate; providing a first laser beam;directing the first laser beam to at least first and second mirrors;reflecting the first laser beam to form at least second and third laserbeams by the at least first and second mirrors, thereby converging theat least second and third laser beams to obtain a converged laser beamon a same irradiation area of the semiconductor film; and moving saidsubstrate relative to said converged laser beam in order to irradiatesaid semiconductor film with said converged laser beam, therebycrystallizing the semiconductor film.
 36. The method of manufacturing asemiconductor device according to claim 35, wherein each of the firstand the second mirrors has a curvature.
 37. The method of manufacturinga semiconductor device according to claim 35, wherein each of the secondand the third laser beams is totally reflected.
 38. A method ofmanufacturing a semiconductor device comprising: providing a first laserbeam; directing the first laser beam to at least first and secondmirrors reflecting the first laser beam to form at least second andthird lager beams by the at least first and second mirrors, wherein thefirst and second mirrors are arranged so that the at least second andthird laser beams are converged wherein an energy distribution of theconverged laser beam is better than that of the first laser beam; andscanning a semiconductor film with the converged laser beam, therebycrystallizing the semiconductor film.
 39. The method of manufacturing asemiconductor device according to claim 38, wherein each of the firstand the second mirrors has a curvature.
 40. The method of manufacturinga semiconductor device according to claim 38, wherein each of the secondand the third laser beams is totally reflected.